The intricacies of game mechanics

Well, you can run another test: if the map is completely empty (and the player is strictly separated from the AI), the AI will run around the map until it explores the entire area, and then it will stand still. If you give the AI a Grail in a tower right away, for example, it won't move at all. The fact that it sees heroes and cities of other players is quite possible, and I've seen similar checks. But most likely, its vision through the fog of war is limited to this. The AI doesn't see what's in chests; it always relies on an average amount of gold or experience. It does see artifacts worn by other heroes and their exact armies. It also sees the guard and reward in banks, but it doesn't distinguish between different artifacts in the reward (i.e., the value of the artifacts is determined by their quantity).