I think it was an instinct reaction. He got hit in the helmet and thought the stick touched his face. Maybe he played a little when he went to the bench and started touching his face, but maybe it was because the ref had already called the penalty and it would've been bad to just skate to the bench and sit as if nothing happened after his initial reaction.
If the player skate (like Cooke) is making any motion that helps the puck get into the net then its a no goal. Cooke clearly turned his skate in a way that helped the puck get into the net.
If the player is standing and the puck hits his skate and get in then its a goal. You can't start taking away goals that get in after hitting standing players who can't really see it coming and don't have any control on where it does hit them.