> The level of sophistication of science in medieval Europe may be way ahead of what we assume (have we even tried to measure it?).

I think he's not gesturing towards medieval Europe, but Rome. There was one empire which was extremely interested in the Mediterranean, the Black Sea, and England, and was bound together by ship, put a lot of effort into improving travel and logistics and measuring distances, much of which's science & math has been lost (leading to regular surprises like the Archimedes palimpsests and the Antikythera mechanism), whose maps could have lasted 800 years or so to be rediscovered by medieval Italians.