My guess is someone at Amazon US entered the 5th in their inventory control system as the release date. Once the item left "pre-order" status and went live because the supposed release date arrived, the system then checks inventory and sees no CDs. That, in turn, simply triggers an "Out of stock" notice. In other words, they have had the date wrong all along and the reason they have no CDs in stock is because they weren't shipped any. And the reason they weren't shipped any is because it's not released yet.
I'm sure all of this is automated and there is little human involvement. With the millions of products they handle, it's doubtful a real, live human being will tend to this. I'm sure they will ship the CDs when they get them after the 25th. I hope it doesn't discourage people from continuing to buy the CD in the interim.