What you're describing is hunter-gatherer (which IS a different civilization, in my opinion, from urban/agriculture) even if it's happening on the fringes of some other civilization.

As far as i know, and I'm not a historian, there haven't been farming (rural or pastoral) civilizations without some town or city involved, farms have always been the umbra of the city.

There were nomadic herders, hunter-gatherers, and farmer/city-states, but there never were cities without farmers nor farmers without cities, ever. So I say they are part of the same civilization even though they are in tension within that system.