Asking for a kiss isn't the same thing as asking to be (description of the patch 6 kisses)
slapped/choked/bitten.
It makes perfect sense if Tav/Durge is surprised and upset if they ask for a kiss and that happens to them instead. The same can be said for players. They only consented to a kiss according to the text, not anything else. In my playthrough I only asked enough times to see all the new kisses once, not 20 times. So it made perfect sense for my character to look upset.

I strongly disagree that this route depicts BDSM. There's nothing to show that this is meant to be a BDSM relationship in-game. Here's more information about how BDSM is actually practiced. In the game, there's no discussion of the dynamic beforehand, safe words, check-ins, aftercare, etc. All of which are practiced in BDSM to ensure everyone's safety and enjoyment. If Larian intended to depict a healthy BDSM relationship, they should add some of these things in order to educate people who don't know what a healthy BDSM relationship should look like. Otherwise, it perpetuates a negative and incorrect view of what BDSM actually is.