Birds of a feather ....
I disagree about the tape recording on 3 counts. The fact that she could modify her behavior doesn't negate the fact that he behaved the way he did. She also would have told on herself if she always goaded him into it as claimed. Modified or not, her behavior is on display too.
Further, there was nothing in the world preventing him from doing the same thing. In this day and age we all know we can be filmed and surveilled at any time and that video can be used against us, even in our own homes. He may have. That may be evidence coming up.
Lastly, it proves the texts were not just "jokes". It backs up the other stuff, establishing a clear pattern of behavior. So even if he knew he was being filmed, it's unlikely he would.have altered his behavior, especially when "the monster" was in control.