For the purposes of this discussion, this is a distinction without a difference. “Black voice” is a term of art, meant to convey that the voices in question were trained on features commonly associated with African American English. The voices in the example are US English voices.
Race, ethnicity, accent, language — all of these are complex topics with plenty of nuances. Short of writing a dissertation, no simple reply on a web forum will appropriately capture them. The good news is, we don’t need to, since most Americans are familiar with African American English, whether they know the term itself or not, because African Americans have constituted a distinct culture in the US for all of the country’s history.
