I think you're reading too much into it, after all it's just a smile.
So I'm bisexual and this girl I know is straight and has a boyfriend but then she smiles at me a lot and she tells me she's bisexual, why?
Slightly tricky question.
Depends upon what you mean by related.
One definition: Connected by common ancestry or sometimes by marriage
But not in the sense of "DEGREES OF KINSHIP BY CIVIL LAW.