If there was ropeplay as well, or ropes used in any way, would the police not find evidence of that? Depends on how early on into the situation it occurred, but of course, knowing CwC, if he literally tied up his mother, there would be marks.
Saying that, it could also be CwC talking shit, so who knows. I'd actually just go with the BDSM stuff being CwC talking shit, but these texts were from earlier on in the week, no?
Ie, they knew on Tuesday that Barb was being sexually abused, and its very likely that they knew earlier too, because there didn't seem to be shock or anything else like that.
I think its likely that they are just releasing the really dirty sounding stuff + the audio recording, but that earlier on in the month Chris probably said something more casual about the sexual situation he had with his mother, and they don't want to release it because it wasnt solicitous enough (based on wanting to break the internet), plus it incriminates them based on the issue that they knew the sexual relationship was going on for a long while, and that they just wanted to wait till they had solicitous audio/texts to release to the public to "omg we broke the internet".