Correct me if I'm wrong, but I thought a himbo was a sort of big beefy guy with a schlong who's kind of a dumbass but an absolute sweetheart and super chill.
I've yet to see a single trans man come close to meeting that criteria (even putting the schlong aside).
The answer is porn brainrot. A guy who likes looking at a pretty woman in high heels, exposed to too much porn, will suddenly fixate on women wearing high heels and eventually it stops being about who's wearing the high heels (or maybe doesn't even need anyone wearing the shoes and just jerks off at a pair of stilettos). He's not exactly gay if he's jerking off at a man in high heels, because he's too perverted to really have a meaningful sexuality. I think the same thing is at play here - Gregory was a gay guy, but now such labels are irrelevant because it's overshadowed by his trans journey.
Although I'm willing to buy that HRT will fuck with people's sexuality, too. I know loads of trans people who turned bi or even to the opposite sexuality, and it's not all just that AGP "I'm attracted to men having sex with me because that reinforces my vision of myself as a woman" thing.