He didn’t use “gang violence” as short hand for “black violence.” That wouldn’t make sense in the context of mass shootings. He said “Counting or not counting gang violence?” more as a shorthand for “Are we counting criminals killing each other?” Whether it’s hispanic, white, or black gangs isn’t very relevant.

Gangs contribute to the majority of designated “mass shootings,” and are often excluded from conversations that want to focus on innocent victims of mass shooting as opposed to cases of criminals killing each other. After all, if all mass shootings were just gangsters shooting each other, people wouldn’t care nearly as much as they do now. They care about the mass shootings that don’t involve gangs.

EDIT: Seems like many sources explicitly exclude gang violence in their stats. So my statement may be incorrect that gangs contribute to “designated” mass shootings as they are not designation such by many sources.