Well, given that Ra kind of is the sun, they wouldn’t be wrong in that assumption. Though that’s not actually what they believed. They believed that Nut was the sky above them, and Geb the unmoving ground beneath, and that they delineated creation. It wasn’t until the Greek Eratosthenes’ experiment that the idea of a round earth was proven, though it had been suggested philosophically for a couple hundred years before him. The idea of the earth actually moving was also proposed by Aristarchus near the same time as Eratosthenes’ experiment, but wouldn’t gain wide acceptance, let alone be proven, until the time of Copernicus, Brahe and Kepler.