Question for GT parents about public disciplining

Also if this turns into an argument about discipline or something, I'll just delete it.

Today I was in a park and this kid, maybe three(?) was jumping from bench to bench along this path. I happened to be sitting in one that was on his path and completely not paying attention to that direction, not that I probably wouldn't have preemptively moved anyway because the only thing that really annoys me about this episode was that he was allowed to put his shoes where people sit.

Anyway, he asked me to move (politely, I should note) so he could continue his path. His mother came running up saying "SonwhosenameIforget, don't you dare! We don't tell people to move!" And I guess it was societal conditioning that made me laugh good-naturedly and say, "Oh, it's ok!"and move. (And it was ok, just moving my ass for two seconds isn't a big deal.)

But right afterwards I was thinking, is this helpful? Wouldn't this piss me off if I were a parent and some bitch directly contradicted my reprimand? Should I just have been like, yeah, in your face, kid? Is being polite actually being rude?

This has happened a few times when I've been indirectly involved in a child's disciplinary moment, and I'm wondering what the best reaction is from a parental perspective. Not having kids myself, it's hard for me to maintain the stoneface and not take the easy route of comforting/placating the child. The only children I know personally are the ones I get to spoil, so.