The problem is that you seem to be condensing this down to a he said/he said issue, when in fact there is going to be more to it that just what each party claims. Apperson, on going for a Stand your ground defence, will have to prove that on the balance of probabilities he had a reasonable fear for his life. With the shaded windows of GZ's vehicle, that is going to actually have to start with him being actually able to see what GZ was doing through those windows, and depending on the light, that might be impossible to do. The police I am sure have already check these sorts of things out, but we simply don't know what they found.
That they are charging him with firing "without provocation" indicates that at the very least they think that they can prove beyond a reasonable doubt that GZ did nothing to provoke Apperson, and I doubt they are basing that purely on the testimony of GZ. So if they are right (and no I'm not saying that they are because we haven't seen the evidence yet) then it would seem that any SYG defence which would have to rely on provocation would be a very high mountain to climb, even without the testimony of GZ. As such, I believe you're merely jumping to a conclusion because of your stance over SYG laws without actually fully understanding the bar that is required to reach, and the evidence for and against it in this case.