It's possible Brunson is confused about what child locks are. Maybe Davis tried to get out of the car but it was locked. But if the backseat passengers are able to get out on their own then the child locks aren't on.
Also, I think it's actually good that the boys are admitting to things like their music was too loud, Dunn was polite when he asked to turn music down, Davis was cursing, etc. it shows they aren't lying or exaggerating. So far, Dunn's version sounds like a gross exaggeration. NO ONE has said he got out of the car, threatened to kill Dunn, had a gun, nothing, not even those who could see the SUV. That sounds like an add on to make Dunn seem more justified. I still don't see the justification for shooting at a car of unarmed young men.