My analysis, worth just as much as you're paying for it:
Putting myself in his shoes... I see an unfamiliar car in the neighbor's driveway across the street. I know the neighbor in question is not home... that's automatically suspicious, but there could still be reasonable explanations for it. A relative stopping by from out of town, a friend staying there after a fight with their spouse, whatever.
I go over to check it out, not because I'm looking for a confrontation, but just to make sure things are all right. Still suspicious enough that I'm not going to go there unarmed, so I grab my trusty .45, stick it in my belt/holster/pocket whatever... start going across the street. I'm on alert, but I'm not EXPECTING to shoot anyone. I mean, there's still a good possibility that I ring the doorbell, and their cousin from out of town answers the door, I introduce myself, maybe go in and have a beer... no problems.
But instead, I see thugs piling my neighbor's belongings into the car. Now I'm out in the open, these thugs may or may not have seen me. I didn't call 911 from the beginning because I didn't know the car was full of burglars. I /DO/ have my .45, and now I see one of the bad guys is reaching for something under the seat.
Hell yes, I'm going to draw my weapon and fire. Just because he hasn't started shooting back yet doesn't mean he's not going to. Just because the car's starting to drive away doesn't mean there aren't about to be bullets flying back at me through the back window. I fire, and keep firing until the car is out of sight and/or I'm out of ammo, then I go in and call 911.
I don't really see how this man could've handled it any better, given the situation.