i dont watch hockey but it looks like he was pissed that there was no call when he got hit, and made his way back to the bench. the ref then moves in to his line, and his thinking was something to the effect of "this guys so blind and dumb im not going to try and save him/ his fault for getting in my way" and hits him in a way that puts the player at the least risk of personal injury. he could have bear hugged him/went down with him/bounced off him but he decided to give him the full force of the impact and followed through on the hit. there probably wasnt a way to avoid contact with the ref, but he made no effort in reducing the force of the impact and made sure he took as little force of the impact as possible
its like if youre walking in a mall and someone is coming towards you texting on your phone and doesnt see you, and you decide to just check them so you dont get injured and they fall on their ass and you just keep walking away.