When the main artery in the rear is cut they will normally bleed out very fast. If he was walking and there was no blood even if it wasnt a pass through after the shot, I would think blood would be working its way out quickly, this is based on seeing numerous hits like this over the past 29 years. Based on what he did after the shot and not finding blood would tell me it isnt a fatal artery hit, but I would still look just in case you hit more forward than you thought etc. It happens man.