The African slave trade of slavs? I think she means Arab. Or Arab/Muslim-osphere.
I wouldn't think sub-Saharan Africans ran a lot of ships up to the Baltic or the Black Sea to capture slavs for enslavement. Ottomans, yes. Barbary pirates, perhaps. Of course some of the most prominent of the Barbary pirates were actually raised Christian or Jewish in Europe, and joined the pirates as adults.
And I wouldn't be surprised at all if Europeans also captured slavs for sale to the Ottomans.
“Kidding on the square” as they used to say.