Not sure if I'm misremembering or not but that conversation mentions how they are rumors. How people SAY she does that.
The definition of rumor is: "a currently circulating story or report of uncertain or doubtful truth."
I.e. possibly false. Something that may not be true at all.
You make it sound like it's a fact that she's a prostitute, when it's not. Rumors can be TRUE OR FALSE. And I'm a firm believer in the whole "innocent until proven guilty" thing so I tend to not make judgements without proper evidence, or at the very least keep my judgments light as well as give the benefit of the doubt, and the fact that it is stated as a rumor helps take some of the suspicion away...
Until Chika comes out of a love hotel with a random guy a day or two after her first H-scene...
THAT would be the "until proven guilty" part. It is impossible to deny the evidence your own eyes give you. She comes out of a love hotel... with another guy. Ergo the prostitute rumor is then confirmed to be true.
That wouldn't be as much of a problem IF it was properly built up to. I've mentioned this in a comment I made 2 months ago, but I'll mention it again. I believe those rumors aren't found anywhere else outside of that exact conversation which represents a massive missed opportunity by the dev. Players first see Chika as a goth who is closed off and apprehensive about friendships. When this random "rumor" is then confirmed to be true a day or so after her scene, it blindsides people because they only just discovered it moments ago. Throughout the game leading up to that point, you find NOTHING about that rumor. NOTHING hints that Chika is a "prostitute." It practically doesn't even exist until SHE HERSELF mentions it RIGHT THEN AND THERE.
At the very least characters should've been talking about the rumors throughout the game, which would then allow more of a story buildup as well as an opportunity for the dev to add in hints as to why the quotes around "prostitute" matter instead of the "just trust me bro" excuse that the dev is currently using. That way the players could possibly discover the hints and then build theories around the whole thing. It'd foster engagement in the community instead of discourse like it is now as well as create more trust with the dev overall. Right now all we can do is wait until 0.4 releases and replaying the game right now yields no additional insight into why it's "prostitute" and not prostitute. 0.4 will essentially be the "make or break" update for many people. Resulting in either people forgiving the dev, or a mass exodus away from the game. Plus there's the fact that his trust has dropped in the eyes of many, which I can see resulting in accusations of the dev rewriting Chika's story in some way or another.