Wtf happened?

A couple guys were duelling each other in Van Horn, So I stood at the side and just watched out of interest, One of the guys won, I was still stood there, Doing absolutely nothing but watching, Then the man who won the duel gets angry and starts shooting at me, Then the whole town gets angry at me and starts shooting at me, I was not talking to anybody, Did not have any gun drawn, Was just watching the duel. Wtf is that?!