The gun by it's mere design looked to me to be either a Beretta 418 .25 caliber or could have been a Walther PPK but I I am not sure. Neither one of them have the knock down power to drop a man in his tracks unless a well placed shot.
If we are going to speculate as to what could have happened, well then yes, he could have hurt something. If we look at what actually happened, he thwarted a crime, put the criminals in the hospital where they can now do time and think about whether or not they want to get loaded on meth and go shoot up a place next time?!! I am sure that all the innocent people that didn't get harmed were very grateful and the old man is now answering all the questions that go along with having a recording of you go public.
Everybody has an opinion and not everyone acts on it. It doesn't take balls to shoot someone that is a threat. It takes the resolve to allay your fear of kill or be killed, steady hands, a loaded weapon, eyesight and a finger. After that it's simply a matter of finding the target, breathing and squeezing.
You can "hurt" someone by sending a foul ball into the stands too, or losing control of your car and hitting a pedestrian. I didn't see anyone tell the man they think it was foolish to shoot at someone that is a DIRECT threat to them, at least not anybody that was actually there and was in the unfortunate situation. Maybe those that find it irresponsible to protect yourselves can try reasoning with the armed men if they get lucky enough to prove their mettle rather than just speculate on that of others. JMHO
Hope that helps,
FDC