The rifleman who knows his firearm and the ammunition it fires very well, will be able to engage long distance targets by applying the skills learnt as a rifleman and sniper. And allow for minor problems such as distance, bullet drop, wind changes at 1000/2000/3000 meters, heat mirage, movement of the target, bullet flight time, etc.

Takes a lot of skill to be able to hit the target at that distance, it certainly wasn't a fluke.