TiborasaurusRex and I just put together a video on this topic where we anatomize the shot a bit. It should be live in the next 24-48hrs.
We set up a S&B PMII 5-25x56 and took some video at 3500m. At 25x you can only tell that the target (he had a human walk around) is there, not what it exactly is. Given a PMII on a Tac50 with 750 A-Max's at 2650fps you're looking at over 80MRAD of drop plus all of the other effects.
Short version, given a 120MOA base, 22MRAD in the turrets, ~20MRAD in the reticle for holdover the shooter would have had to dial out to about 7x on the scope to get the target into the optic, which would have made the target nearly invisible. So it's entirely probable that the sniper was actually sighting against a rock and his spotter or more likely another set of folks entirely was helping to guide him in while he walked rounds down to the bad guy.
Beyond the sheer scale of the scope adjustment and hold-off required some of the effects that only manifest at really long range manifest the hell out of themselves when time of flight gets super nasty: Horizontal coriolis drift would have been somewhere around 50ft. A 1mph variance in the wind call would have meant an easy 6ft of miss potential. A 10fps MV variance would have meant a >6ft miss potential. A big change in humidity could have resulted in a miss of up to about 8ft. Spin drift would be around 30ft. Vertical coriolis would have been around 8ft at full value. It would be super easy to miss 15feet high and 100ft to the right. It would have been insanely difficult if not outright impossible to clearly identify, much less hold on, the target.
Point is, start stacking all of those tolerances and we know exactly how it happened. Blind luck. Yes, TONS of skill too but in all seriousness, it was a lucky shot. Beyond that it was a confirmed kill. Anyone that knows about that process knows that either your spotter sees the target drop or someone walks over and confirms the dead body but another person does the confirming. A sniper ain't likely walking 2 miles right after an engagement TOWARD the enemy to do confirmations. It would be completely normal for these guys to have been on one side of a valley and for some squad to squawk over the radio that they're taking fire or have a BG spotted & they can't get fire on him and they need some support. They'd call in the spot the bad guy is at and the sniper would start raining in fire.
All of my numbers are based on assumptions about the barometric pressure, temperature, angle of the shot and lots about the ammunition/weapon performance. What Rex and I can say pretty much for sure, the sniper almost certainly couldn't actually identify his target and would have relied on someone else to guide his fire in. Even with awesome S&B PMII glass, there are limits.
