I don't think yer man was "beaten to a pulp"
Self defence is all about perceived threat and when someone keeps coming back at you, despite being asked many many times to walk away you're going to assume this person is a little unhinged and poses more of a threat than someone who, say, accidentally bumps into you and spills your pint. And if you get in a fight with someone who seems completely reckless then most people wouldn't stop hitting them until they're absolutely 100% sure they won't come back at them with a knife or a gun.
I am judging this only by the footage that was posted online, mind you. I'm sure the jury saw stuff that we didn't.