They’re not saying who is it isn’t trans to gatekeep, they’re presenting the idea that some people might be less confused and make different life choices if more people tolerated traditionally-gendered subjects (like clothing and makeup) from anyone without judgement

When an identity seems to be defined by appearance/presentation to those who don't understand it personally, assuming the identity would occur less frequently if social norms were less restrictive does make sense. Like personally I don't think drag would be a thing if it wasn't a bit of a response to gender norms. I mean even if society didn't care about which gender wears which clothes some guys would get dolled up and even do essentially the same performative thing because some people just love to perform, but it wouldn't be the same thing that drag is now and it wouldn't be controversial to bigots. I mean women wearing pants was a huge fucking deal for no real reason and nobody really cares anymore.

But using clothing choices as a reason someone might be trans misses the point that a lot of trans people wore jeans and t shirts before and after transitioning because there is far more to it than the superficial appearance of clothing choice.