My observations are:
1) Head shots tend to have kinetic energy that causes the body to fall at an angle and this is especially true in a rifle shot. The energy transfer causes the head to whip to the side and this creates a direction of fall. It is not the flip them over or blow them back 5 feet as hollyweird would have you believe. However, there is generally some sideways motion.
2) This video is from a far distance and only one angle. Other angles would need to be reviewed before anything more than a guess based on personal experience can be made.
3) This body fall does not display the expected behavior of a head shot. As others have stated, the fall is slow and I did not see enough lateral head movement to indicate a head shot.
So absent any additional information / footage, I would concur with either feinting or medical condition.
Full disclosure - I am not a ballistics or forensic expert.
He feinted a faint?
It's become customary, in CQB, to use a suppressed .22 HP, for head shots.
Range is seldom an issue.
No noise, so bystanders aren't spooked and start becoming more difficult targets.
A .22 HP has enough inertia to punch a hole in and then rattle around inside the skull vault, without as much chance of continuing out the back.
It's a quick drop, since living brain tissue is about the consistency of Camembert cheese and the bullet is about a .5 inch wide after penetration...
Just saying.