I saw the documentary where the ex-boyfriend of Freddie's claimed "Killer Queen" was about him.
It's worth pointing out that in 1974-75, it's highly unlikely Freddie would have answered an interviewer with, "Well, Mr. Journalist, the song is about this man I'm fooling around with, since I'm just now realizing I'm gay, even though I'm still shacked up with my girlfriend Mary."
There's a also possibility that the lyrics were what people call a "metaphor" or "allusion" for this guy. It's also called an "in-joke."
Also: gay men often refer to other gay men, especially ones they are friendly with, with the feminine pronoun, i.e., "she."
There's also the possibility that Freddie said "Killer Queen" was about him to get this guy to into bed. I think the former boyfriend himself said it's quite possible he said to a lot of men!
Then again, if could be about high-class call girl, and Freddie just made shit up afterwards. That would require the least work.