I have a friend who drives a bus. In the four years he's been working, he's been robbed, he's had to deal with the most absurd situations regarding intoxicated passengers, and countless threats have been made against him.
Even if they haven't personally experienced any of this, I'm sure most bus (and taxi etc.) drivers have at least heard the stories. My guess is that in his anxiety the driver saw the victim's pestering as an assault/robbery waiting to happen, and chose to take initiative. Extraversion interpreted as hostility. At least it makes more sense than him just deciding to beat someone up for no reason. Besides, he would know that there's a camera to record the incident. How stupid would you have to be to do this on camera if you didn't believe you were in the right?
Since literally all I know about this particular incident is what I saw in a 90-second clip, I'd rather assume the driver was just paranoid, instead of some raging, racist asshole. His motivation doesn't make much of a difference for the victim, but it does mean that the man just might not deserve to be branded as the dregs of humanity by this angry internet mob.