The "book scene" with the sketch-like pictures of the races is a rather odd hurdle when forming theories of the world.

The thing is, though, is that we have no idea what the scene really is. If the scene was what the kids saw when they read the book, how come none of them found it remarkable? None of them say, "Wow! The book is moving!" or, "hey, it has final fantasy characters in it!"*, they just comment that it's filled with a weird latin.

If you ask me, the sketch-scene was merely an attempt to display the book's inner workings. The book is culling Mewt's (or perhaps all of the kid's) desires into itself. I think it's still very logical to assume that the book has no real ties to Final Fantasy, but merely a magical relic that will turn its owner's deepest fantasy of utopia into reality.

* When Marche meets Montblanc, he comments that he's seen Bangaa in computer games, so it we know that the kids were familiar with the races.