Most likely it was some of his posts about outing other people and posting pictures of people that got Steve's back up. He was warned about it a few times if I remember. Couple that was his self confessed aggressive posting style and my guess is that Steve's patience ran out. As he said, it probably wasn't one big thing but a combination of little things. It's his site after all and regardless of what people think is right or wrong, he can do whatever the heck he wants and ban whoever he chooses.
That twitter response from pap has probably convinced Steve that he did the right thing anyway. I imagine I'll get a similar sort of ban one day. Seems fair to me. He'll reappear at some point I'm sure but maybe it'll force him to reign it in a bit which is probably a good lesson for all of us regulars.