question about trans sexuality

Let me start off by saying I support LGBT rights, I'm bisexual myself, but I am not ignorant to the fact that trans people struggle way more with social acceptance. I  don't want to be someone who is ignorant about this matter, so I'm hoping someone can shed some light on it for me, but why is it that before their transition, a person can identify as gay male or lesbian woman, and then after their transition, they are attracted to the same sex. Like a good example would be Gigi Gorgeous, before the transition, she identified as a gay male, afterwards, a lesbian woman. I've had the luxury of pretty much always knowing that I was bi from a really young age, but could it be like they just didn't know their sexual orientation? It just confuses me, like in Gigi's case, that when in a man's body she was attracted to males (so a gay man), but after surgery and hormones she has now come out as a lesbian woman. Feel free to correct me on anything where you feel my logic my be erroneous, I'm honestly just trying to understand better and I couldn't find a good article on it.