Body counts are usually discounted because they are lies, hopes or exaggerations.  In sniping this is compounded because there is money to be made from being a famous sniper- books, teaching. movies. 

To put this story in perspective. The people who compete in very long range shooting normally(under very good conditions) stop getting hits at around 2000 yards.  At very long ranges the bullet is plummeting downward as well as drifting with whatever wind is present- in this case for 10 seconds and an extra 1500 meters to travel all the while losing velocity and falling at an ever steeper angle. The holdover to account for this would be at least a football field and perhaps closer to two.  Since "one shot one kill" clearly isn't possible at 3500 m how many rounds did he fire to figure out where to aim? Remember there was a battle going on so presumably there was a lot of dust etc. How did he see where his first shot hit in order to correct for the next?  It could have hit 100m away.