Well they released the sequel aka version 2 to the first one so it must have done something. I guess it was "long shot" that paid off its gamble in terms of a "sleeper hit". Puns intended!
What I would imagine is that the game had a lower production cost, and the fact that it is a fairly unique game, allowed for them to get buy selling less units at a lower cost but still be profitable. I played it, it was enjoyable, I also waited and got it on sale for cheap.