Not sure why you think that but it's not true at all.
There are four hits to the arm, two to the head, and, a volley of 6 shots, a pause, 4 more shots.
If Wilson was shooting at Brown fleeing, some of those shots to the arm could have been while Brown was turning around. And/or one could have been with Brown turned away from Wilson.
Wilson is closing on Brown, Brown is moving forward toward Wilson during the 3 second gap. Wilson fires one more shot, Brown tries to get down, one second later Wilson fires the last 3 shots.
The shots to the arm do not change the scenario Brown was trying to get on the ground (or was falling to the ground) when he was killed.