What we don't have is any idea of the physical layout of the shooting scene. Was the good guy 10-15 feet from the bad guys, with clear and unimpeded targets and a completely safe backstop for a miss? Or was he further away, with customers between he and the bad guys, and with a backstop into the kitchen?
Starting a gunfight in a crowded restaurant would be bad. If the bad guys appeared to be calm enough to do the robbery and run with no harm to anyone, I think you sit and watch, and be ready (considering the safety of the customers and crew). If they are crazy and start shooting people, you shoot back
if you can do so effectively and safely. But you better not make it worse than it is.
This guy seems to have known what he was doing, skillwise. It could have had other outcomes.
Remember this?