A non-permanent settlement conceivably could see continuous (non-permanent) habitation for thousands of years. If, as a semi-nomadic group, you return to the same location year after year, generation after generation, and you do so alongside a large number of nearby settlements, with whom you maintain social relationships... Well, it might not have a post office or gate, but it's a dynamic fulfills many of the requirements of a "city".

No one said it had to be a single, year-round, uninterrupted settlement. A seasonal, interrupted, settlement would be no different to an asteroid.