please correct me if im wrong.
What? Which man, specifically?
It sounds like you have one particular person in mind, and I can't speak to that specific case, but I will direct you to this article about human genealogy from The Atlantic. http://www.theatlantic.com/magazine/archive/2002/05/the-royal-we/302497/
In sum, it says that a computer model shows that the most recent common ancestor of all people of European descent lived about 600 years ago. In priciple the most recent ancestor was probably born a few hundred years earlier than that due to the fact that people didn't mate randomly in Europe, but still, the principle applies. And if you could look at the descendants of any random person of European ancestry from 1000 years ago, you'd find that that person is either the ancestor of no Europeans, or ALL Europeans. About 20% of people from that time have no descendants in the modern world, and the other 80% have had their genes spread far and wide throughout Europe such that they are related to all Europeans. Based on that principle, yes, one 16th century African man could be the ancestor to millions of Africans today.
hi! I haven't heard this story, but as /u/Marvelsnevercease says, this claim is not unlikely. This sub has had many similar questions about other people, and the answer is always the same: if a person who lived long ago produced any descendants (say, grandchildren), then chances are that most people in a region are descended from them. I rounded up a pile of posts on the topic here: