There seems to be a nuance (which is missing from the title).
The initial paragraph refers to activities which are prohibited.
Peers agreed by a majority of one to ban videos and images depicting
relationships that would not be allowed in real life.
There's perhaps a little more nuance (sexual activity with a step- partner has as an age of consent of 18, rather than the more-typical age of consent of 16)
They also agreed to bring intimate pictures and videos of adults
pretending to be children in line with similar images of real children.
This is about forbidding the depiction of such activity, so I don't think logic will help.