I do cleanup/formatting for a few local authors. A couple of them have gone with KU for some of their books and, yes, they have to be only available through Amazon for those books while they are available through KU. KU does not require that all books by an author be available in KU.
Larger publishers seem to be able to have better deals with Amazon but I am talking about indie authors whose leverage is non-existent.
And note that your example was published in 2011 and is probably grandfathered from before the current KDP rules were in effect. Can you find an example for a book published in, say, 2021?
You might want to read
What to Do if Amazon Shuts Down Your KDP Account and pay special attention to the item titled
5. Enrolling Books in KU that Are Available Wide. One of the authors I've worked with ran into the issue where one of her books was pirated and Amazon suspended her account and she spent quite a bit of time convincing them that this should not affect her account.