Trying to understand bells and whistles of my camera - Sony RX10-IV. I did change metering mode to center. ISO is set to auto. Attached raw file was shot in full sun, still camera choose ISO 6400 .
20240901_0052.ARW (20.0 MB)
Attached file is licensed Creative Commons, By-Attribution, Share-Alike.
Maybe the sensor/software thought that it would need a high ISO because the aperture was set at f16?
The spot meter may have focused on the woods behind the subject prior to shutter release and required a high ISO to capture what details it could.
All speculation on my part…I’m still barely past the “figuring out how to turn the thing on” phase.
'Swhy I haven’t warmed to auto ISO. I’d rather ruin my exposure myself than let the camera do it for me… 
The answer is fairly simple for this. The camera has really over exposed the image because it set the exposure for the dark trees in the background and not the sunlit subject. I note that you have set the meter to centred weighted. This is not a mode I have tested since the days of film. However, when I set my metering to spot I need to ensure the spot is over a mid-tone in the correct lighting for the subject. If I had a bride in a white dress and a groom in a black suit I would get huge shifts in exposure depending on if the spot landed on white, black or skin. To avoid such problems I tend to leave my exposure meter set to the widest area option which is matrix for Nikon and evaluative for Canon.
I also shoot with bracketed exposures most of the time so the camera produces a “normal” exposure, a lighter and a darker exposure. With this subject I would expect the darker exposure of the bracket would be best because even matrix metering would be fooled to some extent with the dark background.
Doesn’t the Sony RX10-IV give a preview of the exposure before taking the shot? If it does you could use the EV compensation control to get the exposure closer to correct before pushing the shutter button.
Good luck with your photography. Auto is not always going to be correct in all circumstances.
Customize how Auto ISO behaves:
https://helpguide.sony.net/dsc/1720/v1/en/contents/TP0001584405.html
PS Changed the topic category to Capturing.
Central to answering your question and why the camera behaved like it did, is that the image has been made with 220 mm focal length (FL) which, according to the image information, is equivalent to 600 mm for FF photography. That works as a very long tele lens with a really narrow field of view which then, even in good light, is quite prone to blur because of camera shake (even on a not too sturdy tripod, that is …).
I don’t know what kind of image stabilisation (IS) you have employed, but this fact alone should lead the camera to seek to make a quite short exposure, (the rule of thumb is that (without IS) exposure time should not exceed 1 divided with the FL), and as you can see the camera has actually (fairly sensibly) used 1/250 sec. With the very long FL of the lens, any longer exposure than the 1/250 sec the camera chose, would mean a high risk for a failed image due to blur. (For the FL 1/500 might have been even better.)
Furthermore, you have used Aperture Priority and, as Adam pointed to, set aperture to very small = f16 (which is so small that you may also be getting into the area of recognizable issues of refraction). With this combination of small aperture and short exposure time, the only way to avoid an underexposed image – since the camera couldn’t raise the exposure time due to minimizing risk for camera shake due to the very long FL – is for the camera to raise ISO (= amplify the signal).
(Why you used such a small aperture only you can know. Likely the main subject in your image was the branches and the two small birds in flight (BIF) therein. Normally one would seek to isolate those from the background (which appears to have no significant information to it) by opening up and using the larger apertures (smaller figures) of the lens. Photographers interested in BIFs often spend lot of money and carry heavy teles to get enough light from as large apertures as possible to make the exposure short enough to render the BIFs sharp in the image (and the larger apertures also isolates the BIFs better from a blurrier background due to narrower depth of field). You can see that for the small birds in your image, their body movement, and especially their small fast-moving wings, 1/250 sec exposure was far from enough to see them sharply.)
For your measuring of the light level you have set the camera to Center Weighted Average, as Terry pointed to. My experience is that this normally works fine, though, and I mostly use this measuring mode myself, but I have long experience with the use of exposure compensation (EC). However, in a mirrorless camera with EVF one can see the effect of EC directly.
Here your main subject likely was the well lit branches and birds, but they represent in total a very little part of the measured central image area which for the rest is fairly dark. This means that the camera in sum measures a fairly low level of light. For an image that the camera computes on the basic assumption of being average 18 percent reflective (=midtone gray), this means that the camera in this case arranges for increased level of light = increasing ISO even more than really necessary for the subject of interest, (so your branches/birds seem overexposed).
Conclusion: Afre was right in changing category to Capture.
Larger (largest) aperture + using around -1 or more EC might have brought ISO down to more normal level for a sunny day and enabled even shorter exposure times and minimizing risk for overexposure of main subject. If BIF was your main motive, taking control over exposure time by avoiding Aperture Priority might also be wise.
I would like to thank everyone. Learning lot of new stuff and do have long way to go.
@EspE1 - To tell the truth, I did not even notice the small aperture. Most likely result of my fiddling with knobs and dials and then forgetting about it.
I rarely use auto ISO, but when DOF and shutter speed are critical (i.e., you want them more or less fixed, e.g., when shooting birds in flight) it’s nice to let the camera adjust the ISO to normalize exposure. A sharp high-ISO image is better than a blurry low-ISO image.
Then again, that assumes I ever succeed in getting a sharp image of a bird in flight, so… 
And you can always limit the auto-ISO range to what you find acceptable (at least my low-level Sony camera allows it). I tend to limit auto-ISO to 1600 or 3200, you may want to do some tests to find out what is acceptable to you. (And yes, sharp high ISO trumps blurry low ISO every time).
You may also find that you can recover a lot more from the shadows than you think. That makes some underexposure at lower ISO a possible alternative. It gives you more range in the highlights: increasing ISO means you amplify the signal more. That means that the maximum intensity you can capture from your scene becomes lower. This maximum intensity corresponds to a pixel value of 1 in DT. In raw, anything over that level will be clipped.
Of course, you push that maximum intensity over 1 when you correct for an under-exposure in dt. But as dt works in unbound floating point, that isn’t an issue, filmic or sigmoid will bring those values back into the output range at the end.