You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
And, of course, the least benign reason people might shy away from it is because they find it persuasive. They agree that bathroom panic is transphobia, but this idea that girls are easily led airheads who oopsy into male gender identities left and right sounds plausible.
Since cis folks are avoiding talking about it, there's no way of knowing where that's coming from. Clearly transphobes think it's to their benefit to portray trans men as confused airheaded girls being girls. I hope the first reason is the most common, but it's hard to know.
