Another interesting tidbit, the original creator (from nopal.net) commented on the Inventables post:
Hi Weird Guy - I’m the creator of the Azteca Wars design. I’m a big supporter of fanart and though I would prefer the file not be distributed, I would ask for credit/attribution at the very least. (Some people are under the impression the artwork is open source). - Best, David Gonzalez www.nopal.net
So, it looks like he already knows of this posted file and did not ask for it to be taken down. He did, however, mention that it is not open source and it looks like he only supports it for one-offs with proper credit given.