A lot of questions arise from this snapshot and the explanation given.
If the guy in the truck felt threatened, he should simply drive away. Nobody has overtly threatened him by blocking his path, or trying to drag him out of his truck (lock your doors, man), or throwing bricks through his windshield. He's in a big steel and glass cocoon that moves. So, move it and himself away from the threat. Your description says he pulled the pistol to make the crowd "leave him alone". Were they making threats, or just taunting him? Had the guy in the helmet already drawn his gun, giving the guy in the truck reason to believe he was in mortal danger?
But, he chose to become a threat himself, by opening his door, pulling and pointing a gun, whether he actually intended to shoot it or not. Showing of a weapon solely as intimidation is brandishing; pointing it at someone is assault, pulling the trigger adds 'with intent to kill'. Then comes the murder or manslaughter charge if he actually kills someone, or 'committing serious injury' if he doesn't.
Enter the guy with the helmet on (looks a little like John Lennon). Why he is at a protest and carrying a weapon leads me to think he might have been looking for trouble, as much as being prepared for it. At any rate, He meets what he perceived as a threat to his life with armed force, and might have been justified if he had shot the guy in the truck, depending on the "stand your ground" or "duty or ability to retreat" laws in Oregon. Or, he could have taken cover to protect himself and waited to see if the guy in the truck was serious or not. But he didn't.
Now, it's become a Mexican Standoff, because guy in truck didn't intend to shoot, and guy with helmet didn't immediately answer the threat.
The only thing either of them can legally do now, is put their guns away.
Last question is, who is shooting the video, and are they also armed; and how stupid are they to be that close to a potential gunfight where they could easily become collateral damage?
I'd like to see the unedited video, if you have a link.