It’s weird to assign a sexual orientation to a robot. Otoh, assigning it a gender isn’t as crazy as it sounds. I think people assume C-3PO and R2-D2 are male because that’s how the human characters treat them. Han Solo even refers to C-3PO as “him” on at least one occasion (“shut him up or shut him down”), and someone probably genders R2D2 at some point as well.