I think he did the right thing.
I am ALWAYS for running if possible, even if it means leaving stuff behind. However, I don't believe a dog to be "stuff". I wouldn't leave my dog to be tortured and killed by 5 drunk jerks. Don't fool yourself, the dog will attack them, and they will in turn beat and kill it.
It is VERY HARD to get a growling, barking, pissed off, 100lb dog into your truck to flee when 5 drunk dudes are approaching.
I would also guess the instant you start fleeing, they come at you faster (even if their intent is to just scare the crap out of you) because they assume you are defenseless and scared. Being drunk and empowered by the thought they have you running scared, I wouldn't put it past them to jump into the bed of his truck or stand in the road blocking his escape before he has a chance to get away (I'm assuming like most fishing holes there is only one road). At this point, I believe the chances of someone getting shot, hit by a truck, or falling off a moving truck just got a lot higher.
He kept himself safe while giving the BGs a choice. He made it clear that he was capable and willing to defend himself and everyone had plenty of time to make a good decision before he needed to open fire.
My biggest suggestion would have been to get behind cover before (or quickly after) drawing your gun. That way if they have weapons you have the tactical advantage, you are covered and sober, they are in the open and drunk.
Running is only the best option if you can get away.