Your definition of the blue flag applies to single class racing like Formula 1. In multi-class racing blue flag is being handled a bit differently. You can of course leave the racing line to let someone pass but you should do so if it is safe. But you should not suddenly leave a reasonable line while someone is close relative to the speed difference. This just increases potential crashes. In your case he exited the chicane normally which leads him being on the outside for the next corner. The best advise in multi-class racing is to stick there and let the faster class take the inside.
Concerning the horn personally I think it's really rude when someone uses the horn next to me (friends excluded) and most of the time people use it that way.
Of course he was going a lap down and he acted accordingly before the revenge. You used the horn in two occasions which might have made him angry. And you unnecessarily crashed into him at last corner. After that you drove next to him driving with his speed and used the horn. That was definitely a provocation in my opinion.
But yes he crashed you intentionally.
Dunno what admins will decide but just take the advice I've written especially about blue flag. It will definitely help raising your joy driving in multi-class racing. So see ya soon maybe even on cargame.nl S2.