It seemed like the interviewer (director?) was constantly antagonizing him. If it wasn't deliberate, then the guy is simply clueless about how to have a sensitive conversation with another human being. Yes, Ginger is a jerk, but I was actually surprised that he waited as long as he did before whacking the guy.
The interviewer was LITERALLY begging for some kind of drama and he got it. That's why he's all smiles as he drives away with his bruised nose.
He just couldn't resist the amateur's urge to include himself in Ginger's story.
If you've ever met Jay Bulger....I absolutely don't doubt that there was a lot of antagonizing and poking, far beyond what you saw in the film. He's a cocky guy.
My take is that it was proof in the present that Ginger Baker is a volatile, cantankerous person who is hard to get along with. That kind of thing is not out of the ordinary for him.