So...
1) The video starts with a woman standing in front of the vehicle. She has nothing in her hands and does not appear to present an immediate and severe threat. The vehicle is not surrounded by other vehicles and the driver could drive away, but running over the crazy lady at that point would likely have gotten him into trouble.
2) At some point the woman moves away from the front of the car. At that point, I would have driven away, making a U-turn if necessary. Even if it seems like the situation has ended, putting space between you and crazy people is a good plan.
3) Driver didn't do that. He just pulled up a few yards and got behind traffic again. Oops. Crazy lady is still a part of his life.
4) Driver continues to sit in traffic while crazy lady acts crazy. Still plenty of opportunity to U-turn and drive away.
5) Crazy lady is joined by crazy friends - probably all fellow homeless/addicts/whatever, which shouldn't be surprising but isn't really germane. Guy standing in front of car is doing the "I have a gun" thing with his hand in his jacket. Now is time for the driver to worry about immediate and severe threats. In his shoes I would be ready for a hard acceleration with intent to both stop the attacker - if he does produce a gun - and also get away from the possibility of further violence. A valid argument can be made that the driver is justified at that moment to drive over the guy. The trouble would be getting the legal system to agree with that argument. I personally don't think I would drive over him at that point. I certainly would not produce a gun, let alone begin firing it.
6) It also is important to note here that he is still not wedged into traffic, although he is near an intersection with a red light. I think it is reasonable, in such a situation, to carefully break traffic laws, such as making a right on red (if that is not legal in the particular state) or cautiously running a red if it can be done with reasonable safety.
7) Guy still has his "gun hand" inside his coat. Driver is looking at his cell phone, presumably dialing 911, and now is completely unprepared to respond if the guy pulls out a gun. Oops, again.
8) Guy in blue approaches driver's door and opens it, because it wasn't locked. At this point I'm almost rooting against the driver, because geez.
9) Driver slams door on blue guy. Blue guy is upset and banging on car. Driver continues to just sit there. Guy in front still has his hand in his jacket. IT IS TIME TO LEAVE. Drive into your attackers - because that is what they now are - if you need to, but get away. Do it gently if you think you can afford to, violently if you think you have to and can justify it. Once you are away from immediate danger, pull over or drive to the nearest law enforcement station, and get your report in.
10) But no, driver continues to sit around wondering what happens next. Which is more yelling, beating on windows, trying door handles. Driver finally figures it's time to leave and begins trying to drive away. Black shirt guy jumps onto the hood, driver stops.
11) This is now a new scenario that requires driver to re-analyze. Priority #1: where is "I have a gun in my coat" guy? Did he produce a gun? Then drive. Driver has no obligation to hood guy if his buddy is pointing a gun at driver. Secondary considerations: where are the other "bad guys" and what are they doing? Each one needs a quick threat assessment. Also is hood guy doing anything but sitting there? If so, he's not an active threat and driver needs to be gentle with him. I personally would consider driving slowly away from the scene, for my own safety, without unduly threatening hood guy, but that's another situation where reasonable people can disagree, and a prosecutor could disagree with reasonable people.
12) Finally, motorist drives away with unknown motorcyclist following. Now is time to call 911 while driving to the nearest law-enforcement agency.
Sorry for the long post. Short version: motorist had plenty of opportunities to get away from this trouble before it turned into real trouble. Motorist should have doors locked at all times. Motorist needs to downgrade the importance of his cell phone in his own mind. And perhaps most important for the purposes of this discussion: this was never a go-to-guns situation. The appropriate defensive weapon here was the car, from beginning to end. At no point should he have relinquished (exited) it and at no point should he have tried to supplement or replace it with a gun.