Stonehenge almost certainly wasn't erected by a hunter-gatherer society. Its main monuments date to about 2500 BC, which in a British context is late Neolithic or early Bronze Age (i.e. post-agricultural), and are generally attributed to the Grooved ware culture.

Forager economics may have existed at the edge of agricultural civilization well after the transition, of course, but from associated artifacts, among other things, we can be pretty sure that the European megaliths were put up by sedentary agriculturalists.