I don't watch hockey, I have before but I'm not really a fan of the sport so obviously what I say take with a grain of salt.
That not only looked intentional, but it looked like it was out of frustration. The ref's back was turned when he was skating backward and the player followed through with the hit. Like I have said I've played and watched limited hockey, but as an experienced player of any sport you should know who the ref's are and what's acceptable.
He could have bumped him, he could have grabbed him on the way down. The player and/or the ref wasn't moving terribly fast. Plus add the video afterwards of his teammate walking over I'm presumably telling him he checked a ref, and him shrugging it off like, oh well shit happens.