I was just watching the news and there was a thing about road rage. They showed clips from this video from a few months ago.
From what I gathered from the man's angry words, the guy driving accidently rear-ended the guy's car.
Ah. In that case, the keyword is accidentally. In other words, he overreacted over something silly in the long run.
Basically this. The marine actually cut them off and then repeatedly slammed the brakes multiple times with no warning.