The incident involved the armed woman walking towards the crowd while pointing her handgun at them. It's clearer in some recordings made from a different angle, e.g.:

https://twitter.com/averyrisch/status/1277398535973949440

So no, not a "standoff". Such behavior is certainly sufficient grounds to dismiss any claims of self-defense - lethal force is justified in self-defense when a reasonable person would perceive a threat of imminent death or significant bodily harm; but if you believe something to be a source of such a grave threat, why would you run at it?