It's not your fault, and it's not his fault. Nothing happened. Sure it was a pretty close pass, but it looked like there was just enough space. It's always the responsibility of the person behind to make a safe pass. But with that said, that doesn't mean you're free to go all over the place. You should always be predictable in how you behave on track, especially for a track day.
As a suggestion, which some may or may not agree with, whenever there is some sort of "kink" on a track, meaning a very slight turn on a straight that you treat as a piece of straightaway not a turn (full throttle) and the optimal line is to get really close to the edge of the track as you go through said kink...don't get that close. I've almost crashed multiple times in situations like that because I was about to pass someone and right as I was almost side by side with them, they moved over clear to the edge of the track leaving me no room, in which case you either grab the brakes, go off the track, or collide with that other person. In situations like that, I always leave about 3-4 feet from the edge, that way if there's a guy right behind me planning a pass on me and he maybe misjudged speeds, he'll have enough room to pass me. We have a kink like that at my home track and it's a good place to pass on the inside right before the fastest turn on the track, but it can all turn to shit in a split second if the guy you're passing moves over to the edge.
Here's what I'm talking about (right before turn 3):