It's mind bottling this is still being discussed.
It was 100% the collision with Jones that shook him up. The hit was fairly routine until he was awkwardly ran over from behind by Jones (who he didn't see coming).
Not sure where all the confusion comes from. Even the youtube clip is clueless. Should be "Gaudreau shoved by opposing player, ran over hard by David Jones"
Also, this thread title needs to be changed. It incites hysteria just reading the first few words.