Thus, the question "does it mean you're gay if you crossdress?" depends on why someone crossdresses.

If someone crossdresses to feel more feminine inside, without any overtly sexual thoughts associated with the clothing, then maybe it means they're gay or transexual.

But if they use women's clothing to get their rocks off, that means they're sexually aroused by feminine things. And that's something gay guys don't do.

The data bears this out:  almost all guys who enjoy women's clothing for overtly sexual reasons, they're almost all heterosexual.

(The case of transwomen is more complicated because we don't have very good data on their sexual orientation. However, it is clear that they dress in female clothing because they genuinely feel feminine inside. They may also be attracted to women, but their primary motivation for wearing women's clothing is to pass as female. Getting your jollies is cheap and easy;  genetic women spend a huge amount of time and money on looking good, and it's that much harder for a man to pass as a decent-looking female)