When you engage these sorts of people and ask the right follow-up questions, there's some common underlying concerns that underpin the polite fictions.
I've found that for men, they are scared that the next woman they look at covetously might have been AMAB. Even if they understand that there is a difference between sex and gender, they are scared that their acquaintances aren't, and are terrified of the prospect of being "tricked" into being attracted to someone who they see as a man. For women, I've found that they see men as biologically and intrinsically dangerous, and that a tiger doesn't change its stripes just because they are alienated from masculinity.
Not that I agree with either viewpoint. Being worried about being "accidentally gay" speaks more to underlying insecurities surrounding masculinity, and "men are inherently dangerous" is just misandry. But I'm no longer surprised by TDS.