that's just a man in makeup

Yeah, that's included in GAMP, conceptually. Blanchard collected an anecdote from a man who's ideal erotic target was a person who was completely indistinguishable from a natal woman, but who at one point in the past had been a man man. This falls into the same bucket. Human sexuality can be directed towards abstract concepts.

I mean, this isn't set in stone, this taxonomy. IIRC Joey has dated women and trans women, not men. So I wouldn't lump him into bi, since bi is generally understood to be people into men and women. Sure, you can stuff it into bi, if you want to, but I think it's worthwhile to keep a typology that would indicate the qualitatively different sorts of things then all being labeled bisexual. Especially with regard to the particular fascination that some men have towards trans women. Other things come into play when developing the taxonomy, like masochism. There's a concept called "forced bi" where the male partner is made to have sex with another man at the behest of a dominant woman and finds this activity to be erotic, yet would never pursue men outside of the sadomasochistic context--which is the erotic locus. I think reducing conceptualization of what goes on in fringe phenomena to what sets of natural genitalia people have will elide important aspects. It also has societal impacts, since the guys marching in the pride parade in full pup-play outfits are all equipped with natural dicks and share a common interest in them, but I'd like to focus on the pup-play thing there.

I don't think Joey is a closeted bisexual or gay man, in the classic sense. Now we can disagree exactly what Joey has going on, but it's obvious that something's up with him that's not the norm. He's got his face plastered all over YouTube. His whole family knows that he's engaged to Blaire, It does not stand up to scrutiny to me that he's closeted in any fashion. If he is, that's some pretty wild formulation of internalized homophobia.

In Joey's case, I'm inclined to believe his self-report of GAMP.

I think your thought process touches something along the lines of that GAMP isn't a phenomena at all and men who are interested in trans women, generally, are just plain old bisexuals, albeit very screwed up ones, in terms of etiology and desire?