Here's hoping they do several more printings.
I'm not an expert in the field, but there's a difference between "Books sold" and "Sell Through". When the publisher ships the book to a distributor it's counted a book sold while the "sell through" number is the number that are sold in retail.
The "Sell Through" rate is never 100%. There are returns, damaged books, and other factors that ensure the retail sales never sell 100% of the books. Wikipedia explains this in a bit more detail at http://en.wikipedia.org/wiki/Sell-through
What I am basically saying is that both statements are true - the publisher seems to have sold the entire run (so they list it as sold out) while various retailers still have copies in stock that they have yet to sell or return.
Here's hoping that Cook's Sell Through rate will be close to 100%!
Richard