On the contrary, he ran back with his weapon faced up, there was no reason to shoot him at all unless he tries to point the gun on one of the soldiers. He had to know soldiers are falling back just as he did, he could wait with the fire until he identifies him.
This shooting was a bad mistake and should have been investigated and court marshaled.

Yeah, Wilson was a new guy, that was his first sight of combat action, the first time he'd been in a battle and it looked like he just panicked and took a wrong turn on the dunes when trying to flee enemy fire. Just really unfortunate.
Maybe Wilson shouldn't have charged from the side, and maybe Kovic should've realized that Vietnamese soldiers were in behind his position, and were physically small while GI's were noticeable bigger compared to them, but it all happened in a split second of intense combat - just a summation of how horrible war is.
Imdb message boards - kick someone's ass on the first day, or become someone's bitch.

I can only assume there was so much chaos/fear/anxiety going on that it's just difficult for one to clearly see everything that's going on.
Art as expression, not as market campaigns, will still capture our imaginations