Theory: The Book in Topsy Turvy was held in Eggland

Abstract
The Forbidden Pop-Up Book of Yoshi's Topsy Turvy is not originally held on Yoshi's Island, but in Eggland.

Arguments

 * Argument 1: The Forbidden Pop-Up Book is never implicitly stated to be on Yoshi's Island.


 * Argument 2: Bowser isn't just causing trouble on Yoshi's Island but "all over", such as Eggland; home of the Egglings.


 * Argument 3: It isn't until Bowser invades Eggland and the Egglings escape for Yoshi's Island that Hongo, Spirit of the Forbidden Pop-Up Book, traps Bowser in the book with the island, indicating that Hongo might have observed Bowser for some time.


 * Argument 4: The Spirit Who Loves Surprises (who used to work for Hongo) refers to Yoshi's Island as "Your island" when Yoshi interacts with it for the first time: this might indicate that the spirits themselves have little to do with the island itself.


 * Argument 5: The Spirit of Cuteness calls the Egglings his pals, which could tie the Forbidden Pop-Up Book to Eggland?
 * Counter argument: It might be in the nature of the Spirit of Cuteness to make friends with cute things, but when viewed together with the statements of the other Spirits (who all work for Hongo), his sayings might have more to them.


 * Argument 6: Yoshi pleads to the Spirit of Kindness: "Please return to us our ideal, peaceful land.", yet the Spirit of Kindness doesn't believe Yoshi is heroic or kind enough to do it. Yoshi's are a famously kind race. How would the Spirit of Kindness not know of the kindness of Yoshi's if he lived on Yoshi's Island?