I was allowing for that. Even with just the Palace commerce, it only takes 50 turns to research Pottery and the Wheel on Marathon. The worker gets built while that's happening, and then takes 12 turns to build the cottage.
So you've got 106 turns to get the cottage built, and it can be done in 62. This doesn't even allow for a high commerce location, a high difficulty level, or a goody hut (which could shave even more time off it.
With no luck at all, the AI could have got that cottage up on turn 62. It would then have stood for 210 turns, so it would actually be possible to have just got a town on the turn above. I emphasise again that this is with no luck at all from huts and so on.
No AI exploit here. The AI could actually have got that cottage up 44 turns earlier than it did.