So what is this new game Demigod?

[Redeyes]

Disclaimer:
Above posters are hopefully joking as copyright infringement doesn't work that way.

Gameplay isn't protected by copyright law (though it might be protected by a patent).

Copyright infringement is the illegal reproduction or the derivative work created from an original work.

[JimMorrison]

If they did not use the code, and they did not use the names AND likenesses (remember: these must be used together, and resemblance /= "likeness"), they did not infringe.