It’s not unusual to say something less controversial than what you wish you could say, so it tracks that someone who wants to say “I’m a boy” would say “I’m a girl who isn’t girly” in a time where the truth is presented as less of an option than it is today. It’s not that trans guys and tomboys are the same thing, it’s that the same label can be either true or a euphemism when applied to different people.

What gets me about the original post is it looks like it’s saying I as an unambiguously masculine man could wear a dress and be called ma’am by a stranger and when I respond “I get why you’d say that but I’m actually a man wearing a dress” then there’s an expectation the stranger might respond “don’t be ridiculous, that’s not a real thing. You’re obviously a trans woman.” I just don’t see this kind of scenario playing out.