When you're at the sea isolated, extremely tired/fatigued and dehydrated even, you can experience hallucinations so I'm pretty sure Tidus was just hallucinating
Rofl
Question time!
Since it's now established that both Bevelle and Zanarkand had summoners, is it safe to assume that Bevelle considered Zanarkand's summoners heretics for not following their divinities, but Yu Yevon instead? The "Mage of Zanarkand" that they fight so fervently against, is that Yu Yevon? It seems to fit, since it's said that he has a daughter and hundreds of followers: he is the Mage, with Yunalesca being the daughter.
It makes sense, since Bevelle's old summoners seem to follow different ways than those of Zanarkand: they adopt their divinities' names and call forth the aeon cores' power to summon; whilst Zanarkand's summoners retain their birth names and use the fayth we saw on FFX, directly opposing Bevelle's ways and this could probably be an inciting factor to start the Machina War.
Btw, isn't it curious that everything shady/dark/nasty/whatever about Spira is related to Bevelle?
Their use of machina was blamed for Sin's apparition,
they made use of torture and subjugation to hide their past and coerce the summoners into advancing to the front lines, that's where **** happened in FFX,
they hid Vegnagun under their depths, Trema took the spheres documenting Spira's past
there to destroy them... One could say that Bevelle alludes to Pandora's Box due to all this ****.
EDIT: Why was Kush unwilling to send Valm to the Farplane, and why did she not let Ifarnal do it? I didn't get it either..