This is what I was led to believe by my friend, that Trico (The beast that the boy is escorting) Is actually the last Colossus, and that they are traveling back to the sacred land for him to live there. I have tried looking this up but no one has said the same thing.

Does anyone know if this story follows the roots of its Previous two games?

Given that the only screenshot we had for years was located in Dormin's temple I think that it's a safe assumption that there is a relation between the games.

It's a follow up to The Second-To-Last Guardian actually.

Probably not.