I think that you just caught the book in transition. The prices change often, especially on the originally free books. Many are only free long enough to garner enough people to give crdible reviews, then the price goes up. If the price changes before the book has been moved from the free list, then the price will show despite the list it is on. It does not happen often- but it does give you a reason to check the list at least every other day.\
This is because the books that Amazon offers as free are sometimes free for a short period of time, such as a week.
The story I made up is they don't get removed from the free book offer before the price has been adjusted back to the non-free price. I have noticed this and the length of time the book is in the free sort has never been more than a day. Again just my guess.
What I want to know is how do I end my subscription? The phone number on my bank statement is not in service! Anyone tried or succeeded in ending their subscription to this "Free Kindle Books", please let me know.