That's one interpretation. He also slumps backwards rather than forwards. In JFK Revisited, Oliver Stone looked into the hospital staff that saw him at Parkland Hospital and all of the accounts he was able to find had the back of JFK's head blown out with an exit wound.
Dude, just watch the film. It's so obvious that his head recoils forward and that there's a massive exit wound on his face. Whatever his body does afterward is going to be a combination of simple dynamics and the muscular contractions that would be characteristic of a massive head trauma. If there's a conspiracy to be uncovered, it's not going to be evidenced in the film.
I just did, it didn't look like what you said at all. I did not see his head rock forward. It's difficult to determine if that's a massive exit wound on his face, it could just be blood.
