Didn't know that, because the file "COPYING" says GPL. I think I will replace the sounds and music, probably by something from opengameart.org.
Right now the game is only half ported to Python3. But I like the Froggix code and Python. So I'm optimistic about developing/porting this game.
Edit: Yeah, I know the error. Unfortunately it won't be the last one. But hey, the program's main menu already works.