They weren't drag racing...they were on foot.
According to Thomas's friend, Thomas had marijuana in his possession (oh, the horror..must be a thug, I'm sure this will justify the shooting in many people's eyes) and thought he heard police so he started running. Copley then shot at Thomas (who was outside) from inside his garage.
The CNN article said the police department doesn't know if Thomas was armed...which probably means they didn't find any weapons on the scene including on the victim. This seems a lot like the Jordan/Dunn case (aka..the loud music shooting) where the shooter magically sees a gun that doesn't exist and claims self-defense once he realizes he's fucked (i.e. he realizes that he's hit someone).
And for people complaining about the racial element. Its inherently racial. Copley said this to the 911 dispatcher: "There are frigging black males outside my frigging house with firearms. Please send PD,". No other description..nothing just "friggin black males" as if to say "Of course, I was in danger....BLACK MALES".