Shoot, the ancient Greeks measured the circumference of the Earth with a high degree of accuracy hundreds of years before this orrery would have been constructed.

They worked out that the Moon is spherical, how big it is, and how far it is from the Earth.

The ancients were plenty smart, and their engineering was pretty darn good too. Roman aqueducts, anyone? The precision engineering required to make them work right would challenge many modern engineers.

No space aliens required.