(SPOILER)Off, I beleive. Yes, everyone in Zanarkand was a fayth, but Tidus was not among those. The people who were the fayth were not the people in the dream version of Zanarkand. Tidus was one of the dream Zanarkand's people. So he disappeared when the summoning of the dream Zanarkand ceased. The fayth died, but Tidus just ceased to exist.