Trope Finder

Accidental Hero

First - technically, "tolerance" is not acceptance, and definitely not approval. You tolerate something if you're willing to let it slide, so to speak. To the point - I'd look somewhere around Apathetic Citizens, as the bystander is just minding their own business, not caring about whatever the authority figure is up to (you said "the first person is in trouble" for something, so I assume it's authority persecuting them). Bystander Syndrome could also work (possibly played with, depending on who we're rooting for), or possibly Weirdness Censor if the pursued character is an alien/mutant/wizard/robot/something else along these lines (but that's a long shot). Bait-and-Switch Sentiment might work here, because the crux of it is one character misinterpreting another's actions, but it isn't very specific. I'd say Bait-and-Switch Compassion would be better for your example (Esmeralda, and presumably the audience, thinks Riku is being compassionate, but he isn't). Or, indeed, Accidental Hero if the deed turned out "heroic" enough. False Reassurance definitely isn't it - this is about "lying by saying the truth" and this is not lying at all (he believes what he says, more or less). As for the ignorant bystanders themselves, they may be Book Dumb (not knowing what Romani is - by the way, how could someone be prejudiced against people of whose existence they know nothing?) or simply Comically Missing the Point (if it's meant to be a dark joke). You might also consider Moral Luck (the character is praised/blamed for the result they didn't mean).

Wouldn't Bait-and-Switch Compassion be Riku doing something mean, instead of doing nothing?

I think Esmeralda assumed Riku would be predjudiced, because she doesn't realize he's from another world.

I thought it would False Reassurance because Riku isn't technically lying— he says he hasn't seen a Romani because he doesn't know what that is. Sort of similiar to the page image from OotS. The dude didn't see Haley because he's can't see.

Like, I guess the response that would be most truthful would be, "What is a Romani?", but Riku didn't ask that. He just says no. Lying by Omission, maybe? Or even Spanner in the Works?

The scene is here, starting from the beginning until about two minutes in, if you want to see it for yourself.

The description for Bait-and-Switch Compassion doesn't say anything about being mean, only: Someone seems at first to be worried about someone else or feeling sympathy for them, but it turns out they are actually thinking something very different. Although this may be interpreted that way, granted. False Reassurance is done on purpose (to troll the other character) - this is definitely not it. Same goes for Lying by Omission. Spanner in the Works might fit here, though, as it doesn't require the spanner to consciously try to mislead.

I'd agree that Esmeralda took Riku for a local and assumed he'd be prejudiced because of that (if most locals are prejudiced, it's sensible to assume prejudice in a local you've just met), then got pleasantly surprised. But her mistake here is still the assumption, since (unbeknownst to her) he is not from her world. Still, she had no way of knowing that, and I'm digressing.

Anyway, there is something bait-and-switchy here, definitely. Bait-and-Switch Sentiment is, as said above, general - if you don't need precise specifics, it should work.