[the_mat]

I suspect you're right, though I'm hoping it was done unintentionally, that he hired a company or acquaintance to "promote" the game, and it resulted in bot-fueled reviews and downloads.

The smoking gun is that he had two other games in the top ten, and that happened without in-app cross-promotion. People would have to look-up Flappy Birds in the app store and click on the "also by" link to even find those games, and there's no way enough people would be doing that to place them in the #2 and #6 slot.