Yes, I also saw the video and it seems that when he lands, everything looks ok, but the injury is worst than we though as he will be out for the whole season. Nothing is to blame though, it was really a freak accident, however, the damage is too severe for him. He is still very young and that is a good thing for him. So it might not be a career ending. As others have said, he need to add some mass and muscle so that he can at least avoid this kind of injuries in his lower bodies.
It's something unusual, because his injury was serious, but his reaction was not so ""desperate""
Because depending of the severity (injury), after the incident the person may cry, fall to the ground immediately and not even be able to walk. (Of course, every human being reacts and tolerates pain totally differently from other people, this is relative).
The reaction that Chet had after the incident apparently proved to be something "normal" during the game, I never thought it was something that serious.