I think you are reinterpreting based on what you think peasants and unlearned folks down thru history have all colloquially thought and were taught. I don’t get any clue from the literal readings of Genesis that Moses(who wrote Genesis) thought the world was flat at all. Moses spent 40 days on Sinai in the burning presence of God.
Moses did not “write” the book of Genesis. The bible existed as oral tradition for many centuries prior to having pen put to paper. (how many people in the ancient world knew how to read?) There are many oral traditions and manuscripts that formed into the bible( even some borrowed from the pagan world). To say Moses wrote the book of Genesis, in the sense that he sat down with pen in hand and wrote it, is extremely simplistic.