Surprisng that it comes from him. but he failed to mention the Arab/Turkish role in the slave trade, or that the Arabs had literally consumed their slaves in labor etc. Not many Arab-Africans running around.
Many male African slaves in Muslim countries were made into eunuchs, a process with a roughly 90% mortality rate. The remainder were used as miners, soldiers, etc.
The females were mostly used as household labor.
The sexes were intentionally kept apart, so no native class of African blood grew up in these countries. Nevertheless, there are Arab countries with discernibly African minorities.
Historically speaking, in most slave societies the population of slaves was not self-sustaining and had to be constantly replenished with imports, as in the sugar islands and Roman Empire.
AFAIK, the American south is the only slave society in history to have a massive population explosion, indicating that conditions were probably less oppressive than the norm for such societies.