can you link the thread? the only thread i found was unfinished before they came to the three powers. (this one: http://www.apforums.net/showthread.php?t=10188)
also do you think anybody could publish a book that has the title one piece without oda's permission??
dont know how it works in japan but in europe it is fully possible as long as the author is clearly stated. (iv personally gotten fooled to buy a book i thought was by Terry pratchett but was merely about his fictional world "discworld". Edit: the damn thing is called "A Terry Pratchett Discworld Quizbook the wyrdest link") from what i see OPGT doesnt reveal anything new just repeats everything already published in the manga and acording to the thread it seems it was a chapter rather then a book.