I know I'm late to the party, but I think the lady is just pissed off for whatever reason. And there's nothing wrong with that; like how you might stomp the shit out of a roach if you saw one when you were in a bad mood. Or whatever.
Honestly, the only 'dumb' thing anon did in the whole story was not noticing that Marisa was bullying Reimu.Even then you can't really blame him, animals play rough a lot.