[DanBC]

> They usually don't quite look like their gender of choice

This is confirmation bias. You notice people who don't look like you think they should look. You then think those people are trans, and when you check a few it turns out they are trans. You've confirmed your bias, and now you think it's true.

What you haven't taken into account is all the people who don't fit this pattern: athletic black women who were born female and identify as female but who are assumed to be transwomen (see all the conspiracy theories around Michelle Obama or the Williams sisters), or the people who do pass well that you're just not aware of.