Fridel found that blacks commit twice as many felony mass shootings as whites (50.49 percent versus 22.33 percent), so it’s not surprising that blacks are overrepresented in this group:
In most instances, the murders serve to eliminate witnesses of a robbery, drug crime, or gang-related attack. Due to their general lack of sensationalism, felony killings are not widely publicized despite representing the second largest category of mass murder (Krouse & Richardson, 2015). Perpetrators of felony mass murders tend to be young Black or Hispanic males with extensive criminal records (Lankford, 2016b). With frequent ties to the drug trade or gangs, they operate in pairs or small groups in urban areas (Fox & Levin, 2015; Petee et al., 1997). As the primary purpose of murder is to cover up another crime, felony killers leave few survivors and generally claim four or five victims on average, similar to family killers (Duwe, 2007). … As with homicide in general, most victims are the same race as the offender(s). [References can be found in the original article.]
https://centerforinquiry.org/blog/who-are-mass-shooters-mass-shooter-demographics-part-2/
A new analysis of 358 mass shootings in America in 2015 found that three-quarters of the victims whose race could be identified were black. Roughly a third of the incidents with known circumstances were drive-by shootings or were identified by law enforcement as gang-related. Another third were sparked by arguments, often among people who were drunk or high. The analysis, conducted by the New York Times with data collected by Reddit’s mass shooting tracker and the Gun Violence Archive, used law enforcement reports on shootings that left four or more people injured or dead in 2015. Few of the incidents resembled the kinds of planned massacres in schools, churches and movie theaters that have attracted intense media and political attention. Instead, the analysis, defined purely by the number of victims injured, revealed that many were part of the broader burden of everyday gun violence on economically struggling neighborhoods. … Many gang-related mass shootings began as fights over small incidents of perceived disrespect.
As noted, truly random violence (involving mass murder or otherwise) is quite rare; shootings almost always emerge from personal conflicts and grievances, between friends, lovers, coworkers, and so on.