It could be that he had a Jewish ancestor. But the DNA may also reflect ancestry among the pre-Germanic, pre-Celtic, or pre-Indo-European inhabitants of Europe and North Africa, rather than Black Africans. You find a cluster of that haplogroup in the mountains of the Balkans among the Kosovars and other Albanians. Also in Sicily and Greece and in Iberia among the Cantabrians (though not the neighboring and better known Basques).
In other words, the water is just as muddy as previously...
During the Middle Ages Jews in Europe sometimes converted to Christianity, either willingly or to save their lives. Their later descendants might not know they had any Jewish ancestors.