Clearly he wasn’t targeting his head. Dude came up on him and he reacted by
swing at him to get him off. It was a quick response like dude get off me. He hit him in the head while doing so ...but he was not TARGETING his head. He was just trying to get the guy away from him because he ran up on him. It was a reaction swing or punch.

And it looks even less serious on replay.

Clearly it was a defense reaction because it was from behind...