This is a side effect of how iOS notifications work - or in this case, what happens when they don't work.
I see this sort of error on game center when the notification for a turn arrives well in advance of the actual game data.
It's kind of like when you check email and get a notification (and there you even get some data from the mail envelope - who sent it, date, subject), but the body of the email is still getting processed and send to your mailbox.
On the Mac app store side of things, I've seen this mismatch for hours and even in some cases days when the app gets hung up. The iOS app store is much more mature so I assume the server infrastructure is either coded more robustly or it has more resources and the delay between an update being signaled and actually available for your device to download is less.
As to how to fix it, you can't really send a reset to the app store app and need to wait it out.