It's interesting how authors can write twisted characters and give them legitimately depressing and reasonable reasons for being the way that they are but treat those circumstances lightly and almost comedically- though it's possible that it's just Yoshino (and not the author) taking the fact that Kirishima- who, at the age of ~12, had to resort to being taken advantage of by predatory adults (some who would hang him by hooks to the ceiling??) for money-- lightly? Maybe she thinks he's just lying? Her reaction was pretty insensitive.
What a screwed up background detail... Makes plenty of sense though with the characterization Kirishima's gotten so far. Still, it's a pretty heavy topic.