The concept of sexual orientation has only been around for 200 years. The decision that sexual orientation should be based on one's gender is arbitrary and vestigial. This becomes obvious when we consider the existence of nonbinary people.
Is an enby exclusively attracted to women a lesbian? Did your brain reflexively attempt to consider what that enby's Assigned Gender At Birth was? That'd be bad. The proper conclusion here is that anyone who identifies as a lesbian is a lesbian, including transmasc people.
The synthesis here being: Sexual Orientation has nothing to do with one's own gender.
We can go farther. "Sexual orientation has nothing to do with the gender/s of the people you're attracted to, it is a social concept that is discrete from attraction"
Bracket theory bb, that straight guy who keeps having sex with men and those straight women who experimented vigorously in college really are straight, because sexual orientation is primarily a group identifier
Tbc this is entirely earnest (I am not saying that everyone is really bi though so don't get on my ass about that)