If you have enough to skate to the bench and have a seat you would think you'd have enough left upstairs to not check a ref like that. Subconsciously all players know how severe that is, so even if he was stunned he had knew it was wrong. He was pissed off and hit the closest thing to him which happened to be a ref. We've seen players full on chop guys on the head out of anger, so I don't think it's hard to believe.