:The text is either not from the book, or you did not cite the correct source.  The source you cited is an "about us" webpage that is not part of the website's books.  That page does not expressly disclaim their rights under copyright law.  Additionally, the text on the front page (which is inadequate for this purpose anyway) does not apply to non-books and non-videos. 
 :To register formal approval for using the text despite the absence of the necessary language on the website, you'll have to go through WP:OTRS.  I am unfamiliar with the process, but the basic idea is that the website owners have to send e-mail to permissions-en@wikimedia.org to officially approve its use.  If the website owner has a Wikipedia account (e.g., if you own the webiste), then you need to tell them that in the first note, because it would save a lot of hassle over future things.