That makes a lot more sense, however, it's not entirely impossible for them to find out what users downloaded the app on that day and only target updates for them; they want out of amazon any way might as well break the TOS. They should be logging some type of 'first_install' after every user pings the server for the first time... but I'm making excuses for Amazon.

TBH both parties are at fault. Them for not reading the letter Amazon send WORD FOR WORD and not Amazon for discounting their app to 99cents the day after.