Quoting the page you just linked: "Once sales start dying and a minimum time has passed, I will release the game source code as some kind of open source. "

Sales are not dying and minimum time did not passed. It does not even look like the sales will die soon. He was thinking about releasing the game when the game is dead and abandoned by gamers. Even if you take the above as a promise, the initial condition is not met and there is no requirement on him to do anything.