David is correct about the way the copyleft works, which almost no one ever is: your content never "becomes" copylefted just because you build upon a copylefted work; you must either explicitly license it under a compatible license, be using the original work in a way that doesn't require a license (fair use, de minimis, etc.), or you are infringing.

Just to go into slightly more technicalities: if CAR doesn't take copyrightable expression from CAH, you can license original work in the new game under a different license; the share-alike requirement doesn't get triggered if what you got from the original wasn't something that would have been protected under the original license.

What counts as taking copyrightable expression can be pretty fuzzy, though. I haven't compared the two games--just clarifying the requirement. And practically, it's advisable to use the BY-NC-SA license from CAH if you're at all unsure.