The security guy was not charged based on very careful analysis of security footage of what actually happened plus witness testimony. Skin color had zero to do with the decision not to charge him. That describes the DA’s first decision not to prosecute the guy.
Over the past couple of weeks she was under pressure from activists and the Board of Stuporvisors to “reconsider” (= prosecute him) and to release security video of the incident.
If the OP article is recent, it speaks of her second, confirming, decision. In her press release, she included to security video and a blow-by-blow very lengthy description of what happened and her analysis thereof that underlies her decision.
Both the security guy and the dead guy are black. The only part skin color played in this decision was that many of the activists demanding prosecution are black.