I will assume this was a male against male, one wanting to fight the other. Don't see the disparity in force to justify the drawing of the gun however; I was not there.
In my case I posted, and the OP's, our cars were blocked from a safe exit. Especially my case where he parked horizontally behind me. I could not drive forward or back, and I could not open my drivers side door to leave the car since he was standing in front of it. When you are given no option to flee, and the aggressor is posing a threat, and in the OP's case he put the car in reverse and the aggressor continued to pursue, the presence of a weapon is completely warranted.
As far as people thinking you can not get hurt in hand to hand altercations, a good female friend of mine lost her brother to a bar fight. Got punched in the head just right and died on the spot.
Think of it this way, get something that is about the same density and weight as a fist, stick it in a sock and swing it at something as hard as you can and tell me that is not a deadly weapon. Fights are not like they are in the movies, when you get hit in the head/face more often than not you will be dazed which greatly impairs your ability to react. I have seen more people in fights knocked out from one punch than I have seen people take punches and continue fighting. The human body can take alot of abuse, but we are also pretty damn fragile.