Lol we're still going on about this huh.
Bottom line, Thedas doesn't know diddly squat about the Qun, and assume all Qunari are of the Qun. Don't even know generally that Qunari isn't specific to the big cow men walking around with horns in their heads.
Just for a real life reference, the United States decided to round up Japanese American men and women when they were at war with Japan. Outsiders, no matter how hard they try to be the same are always the first blamed, the first to be suspected. It really does not matter what Bull's capacity was in Thedas at all. When they hear "Qunari. Heathen", they think of Qunari, period. That is how racism works. You really think that even if a sister weren't racist, that connotation wouldn't be present?
If a tevinter magister walks up to you and raises his hands and says "No bloodmage", do you let him sit down and pass the mead? Hell no.
And unless someone has a better argument than "Clothes different (somehow), not a sister", then we have nothing really to discuss. They were presented as sisters. There's not much reason to believe they aren't.
While Thedas is racist there are cases of different species couples, like Arianni and Vicento, one is a Dalish elf the other is a andrastian human. They even had a child before they broke up.
Thats why I dont see the problem in one woman wanting to have sex with bull.
And the sister thing is that I think she is a lay sister, they dont have a celibacy vow, if she was a full Sister, I would have think it was rudiculous for her to break her vow and be so open about it.
But thats just my opinion, didn't want it to cause a discussion.