Legally, you might be right. I don't know; I'm not a lawyer and I don't care enough about this case to learn about it.
But I'm not talking about legalities here. I'm talking about calling this person's moral character into question because he decided to go this route, which I don't really agree with. I don't care that it is built on top of Rockstar's code. Everything is built on top of somebody else's code. Again, not talking legalities here; but I don't see a difference, and don't agree that Rockstar should even have a say in this. They should sit back and be thankful that somebody created whatever this is which might just sell them a few extra copies of the game through no investment of their own.
I don't like DRM. I don't like people charging money for what is built on top of FOSS. But I also think it's the creators' right to choose how they distribute their work. /shrug
Huh. That's actually just straight beautiful.