The problem is not out-of-focus though. If you look at the ear for the ‘person in the right’ that’s clearly motion, which isn’t there on the left side.
Maybe a bit of out or focus blur is there , but there clearly is ‘directional smearing’ on the right side 
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It’s a focusing issue. I’ve seen this many times when my focus off in that what I meant to shot was OOF but what’s behind or in front is razor sharp. Yes, part is “IN Focus” the other not so appears not only out of focus but distorted as though there was a lot of movement while shooting. If movement was the problem, the entire photo would have been affected.
It is what it is. Become creative and try to figure out how to make it work for you. When I make these type of errors, many times I covert to Black & White and the distortion area becomes Mystique. If that doesn’t work for you then consider further distorting that area of photo with a Gaussian or another type filter thereby removing the attention from this area altogether.
I’ve found very few photos that cannot be rescued but it takes a little imagination. In other words, make what appears to be an error work for you.
Oh, 1 last point. If your depth of field is shallow you’ll get that affect. In that case utilize a higher f/stop and adjust shutter speed or iso accordingly.
If you look at the diagram @sls141 posted, if the person were moving “right and slightly upwards” in the diagram, they would be nearly perpindicular to the camera, but moving away from it in the mirror. e.g. vastly different angular velocities even if the camera were not panning.
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Given that the motion blur also affects the ceiling lamp (@kprince this is definitely a motion blur, it creates “tails” in the direction of the movement, which is horizontal), I think both the photographer and the subject were moving, but in the reflection those opposite movements cancel each other out.
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Reexamined the photo and yes, there is some motion blur. With a shallow DOF and slow shutter of 1/10 that says a lot and I wonder about the autofocus area setting? Interesting photo and the feedback is great. I’ll have to see if I can create the same effect.
I’m really interested in how well the Z7 does in area focusing and tracking? For those whose interested, here’s an article that compares the D850 and Z7.
Kevin “C.” Prince
This is it. The camera panned in a left direction, in the same direction as the reflection.
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You are seeing motion from perpendicular angles, from the mirror perspective there is little displacement; the motion is normal to the sensor plane… whereas from the right perspective we can see displacement across the frame.