One possibility on origin (totally made up by me) could be that there were large stones lying around already as debris from e.g. earthquakes, celestial events and such and some groups took advantage of this and later people iterated upon it.

> Traditionally, the inception of Neolithic lifeways in the Western Valleys of northern Chile is believed to have occurred during the early Formative Period (c. 2000 BC)

key word: "believed" re 2000 BC

They also say:

> The chacu and small-scale settlements described above suggest that a range of human groups occupied this landscape from at least 6000 BC to AD 1700. These groups moved strategically across the highlands, tethered primarily to hunting resources, particularly vicuña.

Its simply stated as true.