Not my image. It was taken by a friend of mine and we are both extremely confused.
The subject is sharp when reflected in the mirror on the left side of the image, yet there is obvious motion blur on the right side of the image.
This is a single shot and not a composite. No shenanigans involved, only basic adjustments done.
Is the mirror closer the camera?
How about - the mirror was vibrating and the camera or lens stablised for that part of the image?
The person and his reflection are moving in opposite directions.
A panning shot can render the reflection sharply, while the room is mildly blurred and the actual person is very blurred.
It’s also weird that the small white fridge (?) and red carpet don’t seem to be blurred.
My guess is that it’s not motion blur, but a strong lens aberration. The camera focused on the mirror image. The rest of the center of the frame is OOF due to shallow DOF. The borders of the frame suffer from lens aberrations.
Interesting.
Just a thought: Doesn’t light coming from a mirror travel twice the distance and thus is easier to focus (object-mirror-lens) then light that travels 1 times the distance )object-lens) and is spread out more (=harder to focus)?
Could be one or an amalagm of : 1) different POV on the subject in the mirror vs direct; 2) lens aberration at the edges of the projection circle, 3) some kind of shutter latency, maybe combined with IBIS movement if the camera is so-equipped.
It depends: if the viewer is close to the mirror, the light travels just a little bit more.
Photographer leaning on the mirror ?
(Causing movement on that and not the rest, or even vice versa)
Slight movement of the camera to the left while the person moves to the right (matching the mirror image ).
But honestly : dirty lens on the right side , or a bad lens issue / decenter … maybe a lens with a strong focus curve at the sides .
I remember something like that (looks like motion blur ) on one side of a cheap 80’s Minolta 17-35 f2.8-4. the left side and the center wasn’t bad , but the right side thought me new levels of 'blurry in the corners '.
Don’t think it has anything to do with light travel distance through a mirror and focusing. It doesn’t look like (simple) out-of-focus blur to me.
My guess is on (sharp) fall off in the lens quality at the side , maybe made worse with a bit of motion.
This one 
Edit:
It could be some kind of multiverse too
I disagree. Lines that are vertical in the image spread further than lines that are horizontal, including the fridge and carpet. This also applies to both images of the man. On the left, observe his apparently elongated fingernails.
What camera was used? If it had image stabilization then that has corrected for movement of one face, which is reasonable. Otherwise, the camera was moving sideways at a similar speed to the man’s reflection.
There may also be other distortions, but I think camera and subject movement are sufficient to explain the effect.
Camera Nikon z7
Lens Z 28 2.8
1/10 shutter speed
IBIS - active
Focus on person in the mirror
at 100% the picture has a slight blur
My $.02 worth on this.
Possibly, the auto focus tried to lock onto the profile of the face in the mirror. That distance cannot be equal to the distance of the actual person. So the the mirror is the focal point, which is closer than the person, who is out of focus.
But the smearing is clearly worse horizontally than vertically, even at the centre of the image.
And the plane containing the reflected man and the actual man is nearly parallel to the sensor plane. If one was out of focus, the other would be also.
Definitely looks like motion blur on the right side. I think camera following the mirror image is a good theory 
This is it. Everything reflected in the mirror is equally blurred other than the person, who is blurred slightly more than his surroundings. He moved to the right during the exposure causing his reflection to move to the left while the camera also moved slightly to the left, “panning” along with his reflection.
By chance, were you using the electronic shutter?
whatever the technical explanation is, I just love this photo!
Hi,
there you go. You focused on the reflection, everything else is out of focus. Actual subject is closer to camera than his reflection
