Thorfinn describes landing in North America and getting stranded seven winters (years) after the Battle of Svolder. This is a real battle fought around 1000 CE in the Baltic Sea, between King Olaf of Norway and an alliance of the Kings of Denmark and Sweden. It was the largest naval battle of the Viking age and resulted in the unification of Norway and the spread of Christianity in Scandinavia.
Sasappis is partially correct in his assertion that Native Americans invented popcorn, it actually originated in Peru but didn't become popular until the 19th century when Charles Cretors invented a popcorn machine in Chicago.
Mead is an ancient, alcoholic drink dating much earlier than the Vikings and made wherever its main ingredient, honey, was available. As honey is a naturally sweet substance, if it is fermented till all its sugar is turned to alcohol, it will be very strong.