It's a LOT from a donate button. Donate buttons generate barely any revenue at all, generally speaking. This game must have either got lucky with the crowd that's playing it, or has literally millions of players already.
Oh sure, for donations that's a lot. A good rule of thumb is asking for donations returns 1-10% compared to selling software for a fixed price. So the game perhaps could have brought $70-700k. Highly dependent on the type of software industry though.