The old guy is no fool, but he is crazy.
The astronomy professor is playing a very dangerous game. He's attacking the Koran by pointing out logical contradictions in it, attacking its literal interpretation. Arab astronomers and navigators accepted a round earth over a thousand years ago, and every Arab schoolboy knows this.
What he's really saying is "The scripture is obviously wrong about the shape of the earth, how can we trust anything it says." You can say the same thing about the Judeo Christian scriptures, too. But you won't get killed for it.