This doesn't seem to be a matter or justice, vigilante or otherwise; it seems to have been a matter of defense in a life and death situation.
It's not valid to assert that he should've left the situation for the police to handle, because no police were handling the situation. We may never know what the intent of the suspects was, and we can never know what would've happened if nobody had intervened. The attackers initiated a life or death situation by initiating a violent crime while armed. They gambled human life on their own goals. Regrettably, they lost, but they set the stakes, so we can take cold comfort in the fact that the loss was theirs.