Yes, Kaizen was talking about that scene in the restaurant. Then you went on to explain what a rumor is and said "It's not a fact" so I sought to correct that.
Y'know, because it is a fact.
But yeah, at that point in time it was unknown. However, it was still mentioned. Also I'm guessing Yuka recounted the flashback word for word so technically both of you know she said "Dangerous people pay to sleep with me" when she saved your sister.
It was actually MC and Yuka who had the doubts and assumed she was simply saying that to scare off the other girls. Chika herself however was honest the entire way through. When she confirmed it later on, it's because she knew you had doubts about what she herself said being true.
Also, that's not exactly something that needs buildup. She said it in a natural situation. Y'know, girls being toxic to other girls about who the latter slept with.
That gets it out of the way, and gives a little insight about why she feels the need to stay away from other people.
And then clearing up lingering confusion and misunderstanding.
Players are actually upset about the fact she's a "main girl" that you can "pursue" and a prostitute.
And some even claim that they didn't know until after the h scene. Which you know isn't even correct.