I will agree with your premise, when/if the whack they apprehended admits he saw someone with a gun and decided it best to escape. Right now, each side only views the episode through their own biased lenses. The "negative outcome," of legal gun toters shooting each other did NOT happen, so the anti-gun group can only say, yea but it's gunna happen. The "positive outcome," presented as, "there would have been MORE dead bodies had they not" brought out their guns has yet to be confirmed. 

"She later heard that people other than the shooter had guns, but they did not confront the killer.

“Why wouldn’t they draw their guns and shoot him?” she said. 

To my first post's point, drawing your weapon without "assessing the threat," or "knowing you/yours are in immediate danger, a.k.a. fearing for your life," WILL likely get you killed by either the actual threat (not knowing where it is) or by another legal gun toter, or even the police! I reiterate, if NOT threatened, 1st response is escape!