I don't think you understood why the gunner was watching the injured guy. At 8:29 of the 17:47 video he says "Come on, buddy. All you gotta do is pick up a weapon." From his tone and inflection it seems pretty clear to me he wants to engage the guy because he's severely hurt, certainly going to die, and probably suffering. He can't engage him because he's unarmed, so he wants him to go for some kind of a weapon because he wants to put the guy out of his misery.
That's not even what I got. What I got was that the gunner had his adrenaline pumping and wanted to kill. He was clearly wanting to kill the remaining survivor, and just waiting for the opportunity.
