I get this quite a lot. It's a very wide junction, so wherever I stop, there's room for even a large vehicle to stop either side of me. Then when there's a gap in the traffic, we both move off on a collision course.
Some just aren't thinking, and a little discussion or gesturing sorts it out. Others are deliberately being obnoxious or impatient, and will cheerfully attempt to drive right through me (I think one driver lost his job doing this. He didn't realise his next drop was where I work).
Howeve nice the guy was, benb, I'd suspect he was impatiently trying to get through the junction ahead of you, assuming you'd let him go first or that you'd jump out of the way.