The most likely explanation is that Amazon made an error, they're not infallible, mistakes can and do occur in such an enormous organisation as theirs.
But their prices do fluctuate quite a bit, I have sometimes ordered things when it says "Only 2 left" and then seen fresh stock a couple of days later at a higher price. Other times it's the other way round, they go down.
A lot is to do with supply and demand. I've noticed with books that were published a few years ago that are no longer in print, when they get down to the last few the price rockets. This is particularly true with foreign maps.
What I have also seen on Amazon, and on eBay too, is that sometimes some sellers have an absolutely ludicrous high price on an item. My theory, and perhaps someone with greater knowledge on this will enlighten me, is that the seller is out of stock of the item and prices it this way just to keep their listing open, knowing that no-one will make a purchase; then when there is more stock the price is readjusted to normal. That's my assumption, anyway.