I think there's a tiny bit of truth in there somewhere. Most people are "born straight", but some percentage are born absolutely gay. They may not know it until they reach puberty and begin to have sexual attraction to other people. They may know from an early age. But there are also a certain percentage that are born bisexual. When they reach puberty they can be attracted to people of either sex. If one of those bi people has positive experiences with either same sex or different sex others, and never has any positive experiences with the other sex, they get in that habit. Probably for life. We tend to imprint on our early sexual experiences.

So that would be a case of a gay person "turning" another gay. But that other person was bi to begin with.

Then there are sexual predators who are more predator than sexual. Like the few pedophiles who don't care which gender their victims are. Or the hypersexual psychopaths who rape women on the outside and rape other men in prison.