Self defense shootings are often dynamic and fluid. It takes an appreciable amount of time, perhaps .25 seconds to .75 seconds for the decision to pull a trigger to translate into the gun firing. During that time it is not unusual to have the assailant turn, or react to a first shot in such a way that the assailant is shot in the back.
My guess, in this case, is that the victim, Erik Scott, was shot in the chest, then in the back as the other officers opened up, after hearing the first officer shoot. That does not make this shooting justified.
Several witnesses said that as Scott laid on the ground writhing, the officers shot him again. It’s in earlier threads.