No, that isn't murder. You may not like it, but you have a guy stop in the middle of the road, get out and start yelling in your window. Up to that point, there is no "threat". Once he crosses that line and starts to attack through the window, the rules change.
That truck had nowhere to go. Blocked in front by the asshole who got out, blocked behind by the guy filming, and traffic had stopped on the other side.
There is no rule saying you must use equal force. If you feel in fear of your life or serious bodily harm, you have the right to defend yourself. The guy in the truck had no idea what the guy was capable of, but he was obviously off his rocker to stop and get out like that in the middle of the road. So now he's gonna start an attack, and who knows if he's mental or what he's going to do.
It's not a pretty situation, and the guy should have never got out the car to begin with, but it was not murder. Had he not crossed the line and started an attack through the window, it's a different case.