I would not bet that West African technology in the Middle Ages was leagues ahead of West African technology:
https://en.wikipedia.org/wiki/Mali_EmpireViking ships weren't that advanced. What they could do was navigate at sea better than their contemporaries, incredibly fierce armies that understood the phalanx, and by far most importantly, ships that were both seaworthy (for short spells), and had a shallow draft, which allowed them to sale up rivers.
The Mali Empire left written records, clearly had more seaworthy ships, and some strange ambition with regard to the Atlantic. These are the basic undisputed facts.
Then there are the Mali expeditions into the Atlantic. Consider,
"The last Kolonkan ruler, Bata Manding Bory Keita, was crowned Mansa Abubakari Keita II in 1310. He continued the non-militant style of rule that characterized Gao and Mohammed ibn Gao Keita, but was interested in the empire's western sea.
According to an account given by Mansa Musa Keita I, who during the reign of Abubakari Keita II served as the mansa's kankoro-sigui, Mali sent two expeditions into the Atlantic.
Mansa Abubakari Keita II left Musa Keita as regent of the empire, demonstrating the stability of this period in Mali, and departed with the second expedition commanding some 4,000 pirogues equipped with both oars and sails in 1311.
Neither the emperor nor any of the ships returned to Mali. Modern historians and scientists are skeptical about the success of either voyage, but the account of these happenings is preserved in both written North African records and the oral records of Mali's djelis."
There's also very odd sculptures from around that time that suggest cross-pollination of native culture with African and Arab cultural practices, including ear-shaping and gauge earrings, which made widespread appearances in the Mali Empire and South America in the same time period. (1200-1300)
The Mali Empire also had far larger ocean-going vessels, more knowledge of celestial navigation (although not the semi-mythical "sun stone" technology), and wrote down epics that seem every bit as credible as the Viking sagas.
Someday I suspect we'll identify little dots of attempted colonies by various cultures in North America. I remember when the Viking visits were considered "racist myths."