Most Greeks knew that the earth was round. It was the actual size that illuded them. The flat earth theory didn't really become mainstream until the collapse of the Roman Empire in the West, and even then the educated knew this was false. Prior to the Greeks we don't really see inquiries being made into the actual structure of the Earth. Reality was merely the boundaries of one's hunting grounds.
As far as your situational dilemma goes, I would have to know more on how this man was transported into this situation. It would have to follow some logic based on the laws of physics, otherwise I would have to assume it was a dream.