First of all, why should a demon state its real name? Maybe he was merely playing a game.Or maybe there is a demon named Seth, and it turns out we don't know all the demons yet. Or maybe he was dyslectic and meant to write Set.
It strikes me as odd that just because a name is not familiar, the whole thing is regarded as BS. I think the 'a haunting' show is very sensational and probably not very accurate (but fun!) but there is no reason to assume there is no entitiy named Seth just because Google and stuff say there isn't.
To me, the fact that they didn't show the original footage when 'Seth' revealed himself on camera, is much more reason to believe the story is BS. Seeing that footage would have been awesome!
Wether Seth exists or not, let's not forget that demons are powerful beings and capable of a lot, why should using a different name -for whatever purpose- not be one of them?
As for christian reactions: so, we are to assume demons are evil because the bible says so? That might be interesting if you believe the bible is true, but since I don't, it means nothing to me. Some people view demons in an entirely different way and I am one of them.



