Really?Sounds like a bad situation to be in, but not one where a firearm needed to be involved.
If that doesn't sound like a situation where a firearm should be involved, I don't know what is... No place to flee to as your car is blocked from both ends. Keeping the windows up was a good idea, but that gun better have been out because there is no telling if he'll bash the windows to get to you, draw a gun of his own, or just walk away.
Sounds like microgunner did well by me, but I would have pressed charges for sure.
And it sounds like the cops agreed with you too. That says something right there...