Exactly - his future potential guests may be non-believers that he wants to have on and so he is down-playing the UFO side of things in current episodes to secure their bookings in near future. On the other hand, if Joe wanted to have big name Area51er Dan Aykroyd on again in the future he would have done the opposite (if this hypothesis is correct) and talk up UFO belief (such as shooting down the balloons and playing up the possibility that they're extraterrestrial in origin) so as to secure Dan's near future booking rather than alienating Dan (who is watching the current episodes to see where Joe's at on UFOs) and losing the booking. BTW here is a much better clip showing Weinstein's total jealousy of Ed Witten (comedic gold). Ed seems like a really nice person and his contributions to new mathematical tools (which he invented to advance string theory) are utterly incredible.