I’d say it’s more than just terminology. A drag queen typically cultivates a persona associated with being in drag and sees it as a piece of performance art. There’s no erotic element typically, and passing as a woman is not the objective (although a drag queen is expected to bring a certain amount of skill, craft, and glamour or camp).
Whether it’s exclusively a gay thing or not? Well, there’s Dame Edna Everidge, who is also Barry Humphries, a straight man, but I don’t think Dame Edna ever been described as a drag queen. On the other hand, nobody denies that Divine was most certainly a drag queen.
And of course, you have the term itself, which includes the word “queen” and which definitely sheds some light on the matter.
At any rate, drag certainly has played a very large role in the American gay experience (including for gay men of color with ball culture), far outpacing its influence among heterosexuals or mainstream culture at large.