Political lesbian is a term with a long history of use.
The current idea that sexuality or sexual attraction is always inborn, innate, and unchangeable, as a kind of supposedly known fact, is something that only became an unquestionable assumption since, I would say maybe beginning in the 1980s, and really solidifying in the public mind in the 90s, as part of a particular line of argument for the social acceptance of gay and lesbian people. But it's not a scientific statement. even if many people feel describes their experience of their sexual desire.
Before that, however, it was common to find a much wider variety of viewpoints on that topic, including within the gay community. The focus on the language tended much more about what people did, rather than specifically why they did it. Functionally, a political lesbian was only having sex with women, whatever the reason.
There's a certain sense to this approach, given that we really don't know what is in anyone's head, and the variability of human sexual feelings and emotions, and even the varying quality of individual sexual desire, especially over a lifetime. When you get too much into trying to describe an exact individual experience, you end up with a gazillion different sexualities and the current situation with the flag for every particular way of thinking and feeling about sex.