It's not so much that you need to assume he is making sense - you have to assume certain things to deduce that he is making sense, to see sense in his responses. You have to assume, for example, that when he talks about the world being smaller then, he is talking about the legend-maker's perceptions of what we now know to be a small region of a much larger, essentially spherical, planet. One with continents and oceans distributed then pretty much as they are today, in physical reality. If you thought of him in post 69, say, as referring to an actually smaller, non-planetary world, one lacking the continents and oceans we have today, that would alter your perception of him as making sense, no? If you thought of him as imagining floodwater overtopping the mountains of Sumeria for a month, while the rest of the planet was somehow unaffected, that would alter your perception of him as making sense, no?