This find is not as surprising as the Economist article would have you believe.
First, what was written about areas beyond Europe's periphery tended to lag behind actual common knowledge of those areas by hundreds of years. An example would be the concept of "the torrid zone," part of an ancient Greek climatic theory that divided the world into two habitable temperate zones, two uninhabitable frigid zones (at the poles), and one uninhabitable torrid zone (basically the equatorial region). You had European textbooks being printed well into the seventeenth century describing the torrid zone's literal uninhabitability. Like, literally describing areas colonized by Europeans and integrated into European economies as unable to sustain any human life.
Second, there are many mentions in medieval European literature of pre-Columbian and, in the case of Africa, pre-Henrician explorers going beyond Europe's periphery, directly contradicting the easy school narratives most of us learned about European "discovery". E.g., the voyage of the Zeno brothers [1]. Most of these mentions are just that, mentions. The Marckalada/Markland manuscript seems notable in that it has a bit more evidentiary heft behind it, but my point is that it's not an entirely unique document.
I should add that generally speaking, there's a rich tradition in history of mercantile contact going well beyond the surviving documentary record. The ancient Romans were almost certainly in regular contact with the Indian subcontinent and possibly China through trade, even though the written record is sketchy. Archaeology has helped in this regard. Michael McCormick is the authority in this area when it comes to the early medieval period or so-called "dark ages" [2].
Edit: In history, be wary of any narrative that presupposes isolation. If you dig deep enough, you'll find that it's often written by someone long dead with an agenda. Hence medievalists' disdain for the "dark ages," which are basically an Italian Renaissance construct that got blown up by nationalist Germans in the nineteenth century.
First, what was written about areas beyond Europe's periphery tended to lag behind actual common knowledge of those areas by hundreds of years. An example would be the concept of "the torrid zone," part of an ancient Greek climatic theory that divided the world into two habitable temperate zones, two uninhabitable frigid zones (at the poles), and one uninhabitable torrid zone (basically the equatorial region). You had European textbooks being printed well into the seventeenth century describing the torrid zone's literal uninhabitability. Like, literally describing areas colonized by Europeans and integrated into European economies as unable to sustain any human life.
Second, there are many mentions in medieval European literature of pre-Columbian and, in the case of Africa, pre-Henrician explorers going beyond Europe's periphery, directly contradicting the easy school narratives most of us learned about European "discovery". E.g., the voyage of the Zeno brothers [1]. Most of these mentions are just that, mentions. The Marckalada/Markland manuscript seems notable in that it has a bit more evidentiary heft behind it, but my point is that it's not an entirely unique document.
I should add that generally speaking, there's a rich tradition in history of mercantile contact going well beyond the surviving documentary record. The ancient Romans were almost certainly in regular contact with the Indian subcontinent and possibly China through trade, even though the written record is sketchy. Archaeology has helped in this regard. Michael McCormick is the authority in this area when it comes to the early medieval period or so-called "dark ages" [2].
Edit: In history, be wary of any narrative that presupposes isolation. If you dig deep enough, you'll find that it's often written by someone long dead with an agenda. Hence medievalists' disdain for the "dark ages," which are basically an Italian Renaissance construct that got blown up by nationalist Germans in the nineteenth century.
[1]: https://en.wikipedia.org/wiki/Voyage_of_the_Zeno_brothers
[2]: https://www.amazon.com/Origins-European-Economy-Communicatio...