Civilization V comes with its own mod tools and level editor, which allow players to create their own modifications to the game. With that in mind, it's not that surprising that a Warcraft-fan would re-create Azeroth for it. For now, the mod is played with the regular Civ-rules and units, but hopefully that will change in the future (unless Blizzard start to send out their famous cease & desist-notes).
You can pick up the full mod at Civfanatics.
