There is truth to stereotypes, but this does not mean that somebody should feel pressured to follow one because it’s what society says they should do. A christian gay does not have to become agnostic. A femme does not have to become butch just to be seen as a lesbian (an issue known as Femme Invisibility). A masculine straight girl should not have to prove that she is straight by becoming feminine!
Stereotypes are not a tool for you to find out somebody’s sexuality or gender identity.