And so the Primer begins anew....
I have a deep seated problem with this game, and Sam hit the nail on the head very early on. This game answers questions that did not need to be answered, and raises new, even more confusing questions as a result.
As we progress through the game, Nomura insists on explaining details that aren't important, rather than elaborating on the ones that are. This initial reveal of Sora saving Roxas before he was even born is just one of those details. Not only does this ruin Sora's appeal as The Unchosen Hero, but it comes out of left field. There's nothing in previous games to even suggest the possibility, and doesn't really add to the story.
I'll point out other such details as we go along. This is only the beginning.