Well not to say you're wrong, but sexuality is not a hard line like people like to imagine, but more of a spectrum. Your spectrum can be 99% for women and 1% for men but it is still there. Just 1 exception doesn't break the rule and destroy your whole identity. That being said, as a person who did not read chapter (because that manga is trash), I can't say how it was said and there is a real chance it was presented in a insulting way. I only wanted to say idea itself might not be completely unreasonable.
You have a point. I have to say that I only read the last chapter because of the ""yuri"" tag and one of them said that when she heard a guy didn't pass in a "girl" (who is in reality a boy cross-dresing) because she was wasted (so being a person makes you gay know). A moment later she continue saying that for talking about transgender people "they are like that too, is a gradation". Sly, I can't talk for the rest of the manga because I'm not into cross-dresing and gender confusing things, so I won't read it, but this last chapter really pissed me off in some parts.