From
Justonemore20's experience as well, maybe I only got the no blow job scene because I had already completed the quest. The last handful of playthroughs I have played them in such a way that unlocking the MMF was a goal, not something I avoided.
All I knew was that when I first started playing this section I avoided the NTR like a plague, and had passed all quests, without Bjorn touching Claire.
Until I realized it was just MMF, not Bjorn stealing Claire. So in my head I just assumed it was because of being able to complete the scene without Bjorn getting a BJ, but maybe it's because I just said no.
Justonemore20 are you sure the quest was forced on you?
You go to the old board, you spend the night there, you wake up, and if you want to progress, you HAVE to talk to Carmen when she is talking to Bjorn. Bjorn goes upstairs, and then IF you have NTR ON, she gives you both her quest and Bjorn's obsession. If you try talking to her at ANY other point, she doesn't give you either quest. If you want to progress Carmen's storyline and have NTR ON, then yes, the quest is forced upon you because you get it alongside the other one. If you turn NTR OFF before talking to her, she only gives you her son's quest (I only tested that once).
If you get to that point with NTR ON, then getting the quest is unavoidable, so those who don't like that kind of content but left the switch ON for either curiosity or what we talked about before with Chyo's words in the intro have to either not do the quest, fail it, or swallow it and do the MMF content just to clear it (this of course only hurts people who don't like that kind of content and don't want to do it but have the NTR content ON because they wanted to avoid it by themselves instead of just turning it off).
Edit: This is a nightmare for a very specific niche of people, those that:
1) Despise certain types of NTR (or at least MMF) but left the switch ON to avoid it themselves since the intro said that it was "always avoidable."
2) Want to clear all the quests without having any in the "Failed quest" section of the journal because they are the kind of people who get all achievements in console games.
3) Thought that ALL NTR content (by that I mean quests too, not just the scenes) could be avoided in the game without messing with the config or failing on purpose because of the explanations when starting a new game.
I just happened to be one of those kind of people and be unlucky enough to find out the hard way.
And yeah, I tried the variations. I lost to Bjorn in cards and then said no when he made his offer to spy on you and Claire and failed the quest (I think I failed the objective, but the quest remained in the "current quest" section, but it became impossible to complete since it didn't give me any other objective or was just waiting for me to redo it and say yes this time, the same way you can fail Kate's minigame quest, but if you later do the minigame again and clear it successfully, it is removed from the "failed quest" section and goes to the "completed" section.) I tried telling him no the second time when he asked to join in the fun, and the quest just failed completely and went to "failed quests," and if you say yes, she gives him a blowjob no matter what; there is no menu, just a scene. So yeah, you do it, you ignore it, or you fail it. But I didn't find any way to clear it without going the NTR way.