How likely is this to be real? If real, was this work originally widely read in its time?
An unfinished and unpublished work in an era before the printing press is guaranteed to not have been widely read.
But the voyages to Vinland went from Greenland. And Greenland had a bishop who wrote to the church. And priests sent letters to each other. It is hardly surprising that one seeking to write a book on distant history and lands would have encountered information from so far afield.