I'm going to guess that people are intentionally recording themselves having sex, assuming that they are creating a local recording that is not sent to Meta. Does the light mean "camera is recording" or "cloud services are involved"?
OTOH, Meta could just be desperate for training content and they're just slurping up all recordings by people who've opted into the AI function. It would be great for them to clarify how this works.
I mean, not as if I were to visit such sites, right ... but video recordings can be done in numerous ways. Also on small devices. I mean the smartphones are fairly small.