What I dont understand is why the other driver would brake check and them ram into him? The truck driver got a gun pulled on him. Why would you provoke this guy even more? Why would you attempt to damage his car when he can fire at you while doing it?
Maybe thinking he could disable the guy's vehicle so he couldn't follow him any longer. That can work, but not at those speeds...
My take on the "victim's" motivations are much less nuanced:
Him pull gun on me...him not do that to me...I smash him.