Historical Background
16th century maps reveal a large bay on the coastline of northern Canada, long before the discovery of such a bay was credited to Henry Hudson in 1607. One possible source that cartographers could have consulted is a book, now lost to us, called the "Inventio Fortunate" by a Minorite preist with an astrolabe from Oxford, thought by some to be Nicholas of Lynn (and for convenience sake whose name we'll use).
Nicholas was thought to have journeyed in these northern lands around Greenland circa 1360, returning to Bergen in 1364 in the company of 8 others. If this expedition did take place, and if it did indeed penetrate into Hudson Bay (which I must admit are very big ifs), then we find it corresponding perfectly with the information on the Kensington Rune Stone.
We also know that in October of 1354, King Magnus of the at that time combined countries of Norway and Sweden commanded an expedition to be sent to Greenland to assist in the finding and rescue of any survivors of the West Greenland colony. The members of that colony, possibly under pressure from the Inuits, had disappeared. Magnus selected Paul Knutson as commander of this voyage, giving him leave to use the royal knorr (or trading vessel) and to select the members of his company, even from his own bodyguard.
Magnus, however was deposed the next year in favor of King Hakkon, and wether the expedition set out as planned is unknown. As Norway/Sweden had inccurred great debt due to internal strife during the early 14th century, it may be that Hakkon expanded the context of the mission to include the exploration of new and exploitable lands, or (as the Inuits bear some resemblance to Mongols) to seek a route to Cathay. If this were the case (and this is highly speculative) it would be beneficial for them to hire a geographer with an astrolabe such as Nicholas.
King Magnus, orders to Paul Knutson
Cartographic Speculations, Part I
Motivation for Carving the Stone