If he'd watched the scene in a mirror it's fine and dandy. The fact he watched later makes him a filthy perv equal to a peado.
That's a great analogy as long as he has a magic mirror that only he knows about and that he can secretly look in whilst having sex.
Seriously, the key point is, if you say to someone "fancy coming back to mine for a shag", that is clearly not the same as saying to someone "fancy coming back to mine so I can film a home made porno film" is it? He clearly knows that the two things are different, and that people are likely to answer differently to each question, because he hid the cameras and recording equipment.
These people obviously did consent to one thing, but didn't consent to the other. In the same way as just because a woman goes for a meal with you, doesn't mean they have consented to have sex with you, the two things are different, so it is at least polite to ask. And whilst it is obviously not equal to having sex with a 6 year old or whatever, it is at the least a pretty nasty thing to do to trick people into making sex films, which even if you don't intend them to be distributed, may well end up public in the future (like they did in this case).
Joe