I think I know what he means. Oxtraca, the lusotanan capital reached 6000 a while ago and I received a message saying "town expands" or something like that, but in Oxtraca there is no building available to build in order to get the next patch of buildings. It's a capital after all, it should maybe grow up to 12000. The reason Im saying this is because I suspect the AI's settlements are growing like hell, and mine isn't.

I just conquered and exterminated an Eleutheroi settlement in northern france that was 9000, and there may be more like this. Isn't the AI getting population bonuses? I for once am not.