That's a little misleading--he didn't outright say "Stella is not the mother," but that scene definitely was in the episode. It may have been right after Ted had his discussion with Robin.
I completely disagree--to be honest, the identity of the mother has never really been the cloying issue since season 2 or so. It's definitely more fun to watch the journey here than get the answers at the end. Besides, nobody's saying it has to end once we meet the mother. I'd hate for it to be...