On my first play-through I somehow had an awkward scene with Cassandra even though I never chose any romance dialogue options with her (I was trying to romance Dorian, but couldn't due to his conversation bug). I think it was somewhere near the end-game, and she confronted me on the ramparts and said she couldn't stand all my "flirting" and asked if I was serious about her. I had to decline and tell her I just viewed her as a friend, and felt a bit like an ass on my Inquisitor's behalf.
I think / would guess that it was related to one of the end-game plot points:
and because I hadn't romanced anyone by that point the game was "double-checking" that I didn't want to pursue a romance with her, since it was a point of no return and the ending would be set after that.
So even if you don't choose romance dialogue options the subject might still come up, but the game won't force you into one.