The truck owner had no chance even if he had a firearm. No way to out with three armed assailants who already have the drop on you.
The only thing that would have mattered is if they ordered him into the car. Then you have to take your chances with fighting since once they have you in the car, you are real fucked.
The guy offering advise must be John MaClane in disguise? Having a gun and a shootout with 3 armed guys may have worked if the owner got the upper hand and started picking the assailants off but boy it could have turned messy real quick.
I'm not trying to sound like a badass navy seal or anything here, but if I saw 3 kids coming at me with guns, I wouldn't be assuming they wanted to steal my truck. Having the advantage of concealment and all three pieces of shit in a few degree target area, I think I would have emptied a magazine in their direction and taken off running in the other.
That's just me though. I've seen countless videos of young scumbags like this. As soon as a gunshot goes off, they scatter like the cockroaches they are. They are not expecting confrontation. They assume they will have an easy target.
There is no right way to act though. Everyone has a different level of acceptable compliance.
Once they are around you, though, they have control of the situation.