Summary: Even nomadic aliens are more advanced than humans.
The inhabitants of this planet were mostly nomads, following their herds from place to place, seeking out fresh grazing, making camp for a few days or a few weeks before moving on again. There were a few permanent settlements, where essential equipment was manufactured, but most people preferred not to be tied down.
Unlike similar nomadic tribes back on earth, however, they didn’t have riding beasts or live in tents; their homes were solidly constructed buildings that were transported on anti-gravity sleds.
Martha strolled with the Doctor along the paved streets. Technologically speaking, these people were centuries ahead of earth.