The same thing, no attraction to men nor women, but attraction to femininity, makes you straight but also into gaydens and trannies?
I’m not saying I necessarily ‘get’ it, but then I don’t get much about male sexuality, (turned on by popping balloons? Wanting to be shrunk tiny small and stamped on by a giant woman? Wtf?) but I will try and explain it.
Duncan’s chart is exclusively about male sexuality, hence no explanation for butch for butch ladies.

In the last section, he puts straight in quotation marks, “straight” . He doesn’t do this for any of the others, so he is indicating the nonsensicality of a male who is attracted to bepenised transwomen (who are GNC males) being described as ‘straight’ in common parlance.
He thinks this is better described as ‘gynesexual (attracted to feminine people) homosexual (attracted to the same sex)‘. This acknowledges the potential for a person with these preferences to also be attracted to hyper femme gay men (personally I think most men attracted to MtF troons are GAMPs, a type of non transitioned autogynephilia, so it’s a fucked up paraphilia rather than orientation plus preference).
If you were to plot out the same theory for female sexuality, a ‘gynesexual homosexual’ would be a lesbian attracted to femme lesbians.
A lesbian attracted to butches would be an ‘androsexual homosexual’ and obviously we know that lots of lesbians are attracted to transmen (because most FtM transitions don’t really get far beyond the hairy, titless butch stage anyway).
I hypothesise that the reason female homosexual androsexuals are more common than male homosexual gynesexuals is mostly just taboo, in that they are dismissed by trannies as chasers, and the gay scene is largely masc for masc, so men who only fancy gay male femmes are either shamed to admit their preference or the preference rarely develops due to social hierarchy and group dynamics (or perhaps even something evolutionary biological, similar to how many women are less attracted to men they know to be bi, a common enough phenomenon that bi men find it advantageous not to mention it).
The taboo aspect would also explain the relative popularity of shemale porn compared to the lack of willingness to date transwomen (although that would also be explained by the fact that mental illness is rarely sexy).
As for the being orientated to neither males nor females, but having a preference for femininity or masulinity, I’m guessing that’s describing people with no real impetus towards sex at all, just wanting the companionship of a partner? I can definitely see how a crazy old cat lady who really wants to fuck no one could end up living with a transwoman, a non-convincing transman or another woman (you can probably find someone like that on most roller derby teams, or hate-reading the farms) but I admit, I find it harder to picture a male example.