A target is a single number. What your camera lightmeter does is measuring the average luminance over some picture region(s), and anchors that to its 18% value (single value -> single value). Even in digital (except for newer models that have an highlight-priority spotmeter). That’s the definition of correct exposure, which comes from the assumptions film used, which are still needed if you use your camera the JPEG way, because 18% is a special place in the (film-like) hard-coded tone curve the firmware applies.
If you use your camera the raw way, such definitions are meaningless. 18% is not a special place. What you need to do is slide a full range (the scene dynamic range) into another full range (the camera dynamic range) by taking into account both extrema and weighting, arbitrarily, which one is the most important (as in : where are your important details located along the luminance axis).
This is not a target. These are 2 opposite constraints to solve concurrently, with some educated guess to favor one rather than the other, while taking into account the property of your specific sensor at the ISO sensitivity you are using it and accounting for possible future changes in lightness in the current scene you are photographying. (Same as audio recording : gain/volume is ok until someone coughs – you may want to plan for that).
There is nothing on your camera that allows you to do that, since even the histogram is showing the JPEG.
The starting point of this article was people found odd to have to push software exposure compensation in seemingly “well-exposed” pictures. That’s not intuitive if you think exposure is an absolute target to reach. The whole point of the article is to say that, in software, it’s only a matter of anchoring middle-grey where you need it on your screen, whereas, in hardware, it’s only a matter of dealing with dynamic range clipping.
So, indeed, there are not underexposed pictures, per say. There are only clipped pictures (at one end or at the other, or maybe at both). And so, the whole concept of hardware exposure needs a rethink in terms of range, and not in terms of anchoring individual values.