Ok...so lets go hypothetical then. Lets say the guy TRIES to grab the kid. (The "kid" being roughly the same size as the guy...)
The kid resists. He's probably going to try to punch the guy, or try to break free and run. First off, in this hypothetical situation the guy broke the law by grabbing the kid. What happens next?
Case one: the kid DID break free and probably hit the dude and ran...and would most definitely be calling the cops because some whack job just tried to assault him in his own neighborhood. If the guy pulls a gun at this point and there are ANY witnesses, then the guy just pretty much screwed himself. If the kid or anyone else can describe the gun that the man was carrying, he's going to be in some serious trouble with the law enforcement. His gun toting days will be curtailed for awhile, or not be over entirely. If the guy shoots at this point, he's going to put a bullet in the kid's back. Also...not a good thing for when the police arrive. He'd be definitively screwed.
Case two: the kid didn't break free. Seriously...how many hands does the guy have? He's going to hold a guy his own size captive AND draw a gun on him? How the hell would that work? Again...the cops get there and the guy who did the grabbing is likely going to be taken away in a police cruiser. The kid and his family are probably going to press charges.
In either case, if there were shots fired, it would be kind of obvious what happened when they study the ballistics, etc. The distance he's shot from, the angle he was hit at, etc. If he shoots the kid in the back...bad news for him when the cops get there. If he shoots the unarmed kid from some number of feet away...again...obviously bad for him. If he shoots the kid after the kid knocks him down and was beating his head against the pavement - well - I don't know many self defense cases that look like that. Getting on top of someone and beating the crap out of them isn't a typical self defense scenario...
Bear in mind...all of these things are playing out in a residential neighborhood with people nearby. When they start hearing the commotion...they're going to show up. Neither of hypothetical situation is going to go well for the guy here...and he'd know that going into it. It's kinda obvious. And it's why things were really unlikely to have gone that way.
That's the thing with the stand your ground laws...you don't HAVE to retreat under the law, but that's not the same thing as saying that you shouldn't. You damn well should try to de-escalate the situation...and both parties were old enough to know that. It's kinda like the old saying that having the right to do something is not the same as being right to do it.
Both parties were being idiots, but most people here are polarized about it - they only see one of them as having really messed up.