According to Ed Bozinski, Bible writers and ancient Near Easterners generally were rubes and hicks who all thought the earth was flat because they didn’t have access to satellite photography. They had to go by appearances, and to all appearances the earth was flat. (Or so goes the argument.)
Well, let’s consider a simple counterexample. Anyone living on the coast is in a position to register a correlation between the lunar cycle and the tidal cycle. Indeed, if you were, let us say, an ancient sailor or fisherman, you’d have a practical incentive to take note of that correlation.
As we all know, tidal action involves a complex set of motions which include a spinning spherical earth in relation to the sun and moon–as well as other variables.
But just imagine trying to create a geoplanar model of the tides, where the dry land is swimming in a saucer. It wouldn’t take a knowledge of satellite photography to realize that this is not a terribly realistic model of tidal action.
Although ancient observers would lack the detailed information to know what, exactly, is the correct theory of tidal action, they already had enough information to know that a flat-earth or triple-decker universe could not account for tidal action.
There’s a difference between knowing that something is wrong, and knowing the correct alternative. We can often know that something is wrong before we know the right answer. Indeed, knowing that something is wrong is frequently the spur to exploring alternative explanations.
Incidentally, although I haven’t studied the subject, I assume the Nile river is a tidal river near the coast.