Great analysis by @zachwill. Thanks to Benedict Evans for the link.

January 22nd Dong Nguyen was probably extremely excited about the couple months worth of revenue his marketing experiment had pulled off. With the recurring in-game ads and 800 reviews in a single day, Flappy Bird was beyond a success. Mission accomplished.

February 1st Dong Nguyen, on the other hand, must have questioned if the world had lost its mind.

On February 1st, reviews exploded to 800 in a single hour. 6,500 iTunes App Store reviews in a single day. February 1st is the day Dong Nguyen woke up, stretched, checked email, checked Twitter, checked iTunes, and witnessed millions of downloads happening.