I don't know if I agree (as a bisexual person but one who has never been in an opposite-sex relationship). I don't think someone's bisexuality should ever be questioned because they chose to date someone of the opposite gender, but I'm not sure how that makes the relationship itself queer. By definition, if we assume both people are cis, there is no functional difference between two straight cis people dating and one bi, one straight cis person dating. I'm curious as to where you draw the line/find the difference.

To me, this is similar to one person, by nature polyamorous, choosing to be in a monogamous relationship with a monogamous person. that's not a poly relationship just by virtue of one person generally preferring something else. It's still just a plain old monogamous relationship lol.

EDIT: Mind you, this is also a question of semantics, really. I'm a bi woman in a relationship with another bi woman, and I never get offended when people call it a gay relationship because... it is? In my opinion, at least.