That phrase comes from people who are either stuck in the closet, or in denial about their own sexuality. It is just one of the many byproducts of a society that still insists on considering that being straight is the only "normal" way of being.
I agree with you in real life, but I do think rogue would play up her bi-ness in a public setting cuz she knows she's hot & is a bit of an exhibitionist. She's also probably had a group break up session where she dumps all 6 of her partners at once in a hipster coffee shop then asks for the batistas phone number.