Yeah I was not a fan of Guns, Germs and Steel which is the only one of his works that I read (and I think mentions the Greenland debacle), to me it’s much more ideological than historical. History just isn’t that deterministic.
It seems most likely that the Greenland colonies were brought down by a combination of climate change and the arrival of large numbers of inuit.
Basque whalers and fishermen were apparently making it out to that area routinely by the 14th Century.