Personally, I'd talk to him once I'm nice and calm and get his side of the story. A number of things could have been going though (or missing from) his mind. Asking the guy "Hey, did you know I was leading the field and you..." isn't threatening, he'll know it was a big enough deal that you came to talk about it. If there's a difference of opinion on what was the right course of action in that situation, you can discuss it, and if it turns out he's just an

you'll know it for future reference.
A mixed group I was in last year played together a lot better by the end of the year than at the beginning. Some of it sorted itself out on the track as people figured out who's fast where. Some involved paint exchanges, and there were a number of discussions...not all bad ones. I had a 911 driver tell me that he saw a few of us racing hard in the final laps and backed off rather than try to get around, which I found rather cool of him. Knowing that, if I saw him in a similar situation I'd do the same.