I have had many discussions with Paul Heinegg. Most of these Free African Americans were themselves children or grandchildren or even great grandchildren of enslaved persons.
I do not claim full knowledge of the subject, but from what I know. The very first Africans brought to the Virginia Colony, were actually captured by the English aboard Spanish Ships, and the Spanish and Portugese were involved in the slave trade.
These Africans were treated in the same manner as indentured servants, and after service freed from their indenture given some land and a musket, just like the freedEuropeans.
It is also a fact that the majority of persons who claim southern ancestry, have European indentured servants as their ancestors The Tidewater aristocrats, aka Planters, had not the werewithall nor desire to do the work to maintain the lifestfyle to which they were accustomed, so they imported tradesmen and indentured servants (male and female).
In the early days of the colony, marriage or cohabitation between personages of different colors was accepted, however what was not accepted was marriage between different classes, and there were only two classes. It was unthinkable that a "white" planter would marry an indentured servant. However a "black" planter, and there were such, not many, but a few, could marry without too much social opprobrium a white.
Indentured servitude for "blacks" went the way of the DoDo with the case of Anthony Johnson v John Casor
https://en.wikipedia.org/wiki/Anthony_Johnson_(colonist)
Those interested in the subject, should read The Fiddler on Pantico Run, it is the story of a freed indentured servant of African origin, who established himself on land he was given when he fulfilled his term of indenture.
He has many descendants today (see the Mozingo DNA project at FTDNA), some are proud members of the KKK and others are "black".
One of them is an established Alabama judge.
As regards the Free African Americans mentioned in Paul Heineggs book, for most that freedom did not last long, for after 1830, and the Nat Turner rebellion, many of them were re enslaved, or otherwise deprived of their property (land and slaves).
For a period of time, until 1830, two states (S.C. and Louisiana) had a large number of "black" plantation and slave owners.
In another vein, while researching records at familysearch.org, I found a distant relative (2nd cousin 4 x removed) whose 1860 tax records mentioned amongst his holdings, a white male 2- to 50 years of age.
The history of enslavement in America is not so simple and one sided, but it is also a fact that this country was built on the backs of indentured and enslaved (even if it was wage slavery)..
Things we learn when history is used in conjunction with genealogy.