The point is you don't need to know the status of people's private parts or chromosomes to call them men or women because that's not how we, as a society, treat men and women. And trying to investigate any potential trans person on their genitals just so you can misgender them would be rude. Which mostly you wouldn't do anyway, as you most likely meet and greet many transgender people as the gender expression they present to you.What point is that? Beating around the bush?
Although it is pretty funny when I get misgendered in the bathroom by pearl clutching conservatives who think I'm in the wrong place just because I don't look like what they think women should look like, but that's a topic for later.