Who do you blame for this one? The obvious answer is the player because he is the one that slugged the ref, but in his defense he had no idea what was happening because he had his jersey pulled over his head. If it was his opponent who grabbed him and he didn't defend himself he would have been in trouble. If anything, this is just an extremely unfortunate situation where the ref tried to jump in and separate guys who just weren't ready to call it quits yet.
This happened in the LNAH by the way. A lower level professional hockey league in Quebec. It isn't well known for its high end talent or star players, and has actually earned a reputation as one of the toughest leagues in hockey because of all the fighters and on-ice antics that take place.