Although I firmly believe you should be able to defend your home, seems to me this guy may be wrong.
He baited. MT law says you can use deadly force if you "reasonably believe" someone is trying to harm you.
We will never know what actually transpired in the garage, whether the homeowner just blazed away, vs being threatened, the victim was trying to return the purse, or at a stretch, the victim was actually stealing from the homeowner. We can't know.
One can certainly understand the homeowner's rage at being repeatedly robbed. I get it. But before shooting someone, I would choose to get them on videotape and prosecute.