I always tell people that we know we are gay and nobody needs to tell us that fact on sites tailored for gay men

"this straight girl shuffs up a dildo up her straight horny pussy to enjoy all the straight sex she can get. Also she likes straight cocks from straight men up her straight ass"

now how does THAT sound like?

IMHO google knows that your site is "gay" if you use it once or twice in domain or title or metatags or on your site.
Google will also know the "category" of your site when crawling it if you write something like "this guy is really into having his butt and mouth stuffed with huge cocks of really hung men".

They are sitting on vast amounts of data to compare sites with each other.

0.02€ cent

Develish