Yes, it was composed of pyreflies. While Tidus existed, it was not a technical existence, since being real is not defined to the people of Spira as "existing at some faraway point in the ocean where your destiny is to live and die and disappear and not to at any point interact with the people of Spira."

Tidus did NOT EXIST 1000 years ago, as a misconception of the game will lead you to believe. He lived concurrently with the rest of Spira in Dream Zanarkand, except far removed.