There's no solid backstory behind this hidden quest. You don't get enough clues about the lore behind the Nameless Island. After completing tasks, the only thing you get is a few lines about a riddle that you have to solve and fight the eye of the storm once again. It's purely my speculation, but I think there may be another part of this quest where we have to find Henry's friend. It might be possible that the island, which is not of much importance right now, becomes vital to the game's lore. All of this is currently my speculation, and I think maybe we will get more content related to the world quest in the future.