Right, obviously, a difficult question to answer because as you know, our arms can do all sorts of things in three dimensional space. And, you know, the shooter versus who is receiving the bullets, it also depends on where they are in three dimensional space.
So if you are asking me could a shot from his backside produce that, I say yes. Because as you are running, if your arm is down like this, that surface, that very surface of your arm is exposed posteriorly. So a bullet coming from behind you could cause that injury.
Could it come from the front side? Yes, depending on how your arm is. If your arm is out in front of you like this, a bullet impacting here could still exit here.
If your arms are up like this, they have to be rotated in order for the bullet to impact here if the shooter is directly ahead of you. It's difficult, but I think there is a lot of different scenarios that can explain that trajectory.