Amazon in error

Here's an article in which the author claims that Amazon lowered his price to free incorrectly (price-matching sample chapters rather than a full book), and now they won't pay him for the 5104 copies he "sold" while the book was free. Well... regardless of whether Amazon made an error or not, there's no way in the world he would have sold those 5104 copies at $5.99. Any observer of Amazon knows that when a book goes free, it can go from selling no copies to thousands of copies in a heartbeat. (Now that the book's back to paid status, it's only ranked at 71,662, which means the author is selling at most a couple copies a day.) Therefore, I don't think the author "lost" the royalties; he just gained some exposure.