Higbee has a mic'd up video from a prior game where he gets hit late or out of bounds and he tells the cornerback or safety on the other team who hit him "I owe you one". Then towards the end of the game, he delivers a crushing blow on the guy away from the play, and tells him "I owed you one" and the guys says "I know" and they were cool.
I think this team takes extreme pride in pay back for cheap shots. This incident sends a message to the entire league that I will hunt you down and get even, during the post game if I have to, so just don't do it. We don't condone it, but Donald felt so disrespected about it, that it had to be done.