Even if it wasn't an April Fool's joke, I don't know that I would take much stock in his speculation on the matter. His area of expertise (nor any of the people on his team) isn't metallurgy, chemistry, history, or archaeology. Its linguistics and Scandinavian studies (specifically the Old Norse language and the Norse myths). He translates the language and can read the runes. He gets his funding through his Youtube videos and patreon so I wouldn't be surprised to learn that he sensationalizes and embellishes things for clicks.