So apparently, the AI is just straight up cheating. Last turn, I took the Macedon warrior down to about 25 hp, maybe even less (he had that little that one of my UUs would have probably killed him, and if not he'd have been at 1 hp for the other to kill him, with a +8 advantage from Oligarchy + Deity). He can have healed 50 hp from promotion, plus 10 from not moving, is 60 hp. Which is NO WAY enough to get him to full health. Also, he did not capture a city with a wonder, his units at the top of the screen are still damaged.