Perhaps this is the kind of attention he didn't want. His Twitter timeline makes him sound like a pretty humble indie dev who is more interested in making games fun than making money. I guess the "fun" part doesn't exist when you get death threats.
He removed Flappy Bird from the App store so that the media would publish headlines like this, increasing attention focused to his app. Then, he has two options: republish, or sell. If he republishes his app, the media will publish another story, increasing downloads. If he chooses to sell the app, he can probably find a buyer in the dozens of offers he is presumably receiving right now (in between death threats of course).
