Victim seemed to react as a last minute thing as he appeared to not be paying attention to the guy walking around with the gun. That's one reason I try and not use my phone in public places as it distracts you.
If the victim or others had a gun perhaps they could have reacted to the guy with the gun before he used it but again they could have thought he might be an LEO and had reason to have his gun out.
I'm glad it worked out the way it did but goes to show you such things happen fast and you don't get much time to react.