“How did he even know what a black man was?”
How did he know what a White Man was in 1451 America?
They said he was a prophet.
There is a mounting pile of good evidence(both archaeology and DNA) that the Vikings were in NA long before Columbus showed up. Possibly as long as 800 years before.
https://www.historyonthenet.com/viking-law-and-government-the-thing
Since the “Native Americans” never discovered the wheel I am not concerned about the prophecy being correct.