He didn't extend his elbow, his stick was right with the puck.
I disagree. You can clearly see his upper hand on butt of the stick and the puck traveling to the left.
Hockey players are taught to keep their elbows down when you stick handle a puck. For people that play hockey know this, your elbow is supposed to be down and comfortable even when reaching for a puck. Your arm is supposed to be away from your body slightly to allow freer (is that a word?) movement.
I play hockey and the only way that happens by "accident" is a error in judgement. Whether he extended the elbow on purpose to knock him off balance or not, he had a DO'H moment that caused it to happen.
Still a penalty should've been called and a suspension will be filed.