Why does femboy = gay?

I never understood why whenever a guy dress or act more femininely he's tagged as being gay. Sexuality has nothing to do with it. And I know it is partially because of toxic masculinity that portraits anything even remotely feminine as bad. But females also do that. They look at a guy and see they aren't stinking of testosterone and misogyny from head to toe and shove a gay tag down their throat. I want to read someone else opinion on it, please.