The AI doesn't cheat pretty much as a rule. If something happens that is out of the ordinary, then it's a bug, not a cheat. For instance, some people (including me) have experienced the AI attacking with two units from within a city. But if you position your units correctly (new siege unit in a city firing, and then another siege unit with nowhere to go, IIRC), then you can do it too! It's not a practical difference, but then the question is, so what if they were cheating? What does it matter? It would be just another way of artificially making a level more difficult, and partially making up for the disadvantage of not being a human.