It is confusing, and I'm sorry if it is taking me a few tries to articulate this.
First, I've seen posts here from CDers who were convinced that trans-admirers (the men who say they are straight, but who are specifically drawn to other men with penises who present as women)** are into them as women. The fantasy to perform as a woman sexually is so strong that the CDer will convince himself that he is a woman who is seeing a man who treats him like a woman, so therefore it is a heterosexual encounter.
Is this CDer gay since he is attracted to men? Or in his delusion of being a woman, is he straight? He thinks he is straight, yet by society's standards, these are two men who are having gay sex. They are homosexual, even though for a time, one of them identifies as a woman. Caveat: if the person who is presenting as a female is a non-op or pre-op transsexual, then she does identify permanently as a woman and so she, at least, is not having gay sex, even though the trans-admirer is. If however the man she is having sex with is not a trans-admirer and he ignores the penis and sees it as much as a hindrance as the TS, then neither of them are having gay sex.
There are too many "ifs".
I spoke earlier of a CDer who knows he is a man, identifies as a man most of the time and considers himself to be hetero while in male mode. If he has sex while dressed with a trans-admirer, they are both most definitely having gay sex since the basis for attraction is the other's penis. Even if this CDer's motive is autogynephilic, he is still having gay sex. If he enjoys his experiences with men, he is not hetero. If he also enjoys having sex with women whether he is dressed or not, he is bi whether or not he likes to admit it when he is in male mode.
If this same CDer has only ever had sex with women and the thought of having sex with a man is repulsive to him, I don't think this would change during an actual encounter with a man, no matter how much he uses a faceless man when he masturbates to an autogynephilic fantasy. In this case, the CDer would not be bi.
** These trans-admirers are not attracted to birth females and they drop transwomen as soon as they have SRS.