Anyone looking at that video who claims the shot came fom behind is a damned insulting liar, and not worth the respect of a reply.
Yep.
The "explanation" always involves theoretical physics, or simply "his chin bounced off his chest", or whatever. Kennedy's entire upper body - - not just his head - - is propelled backward by the force of the shot.
...which obviously came from the front.
The exit wound is where you get the most damage. The force of the shot exiting his skull forces the head backwards.