We will have ALOT more data after this weekend to answer this question.
From my personal shooting, wind drift is what makes certain options poor.
The BMG has the best wind drift characteristics of any 'common' LR rig but it is rarely as accurate. IF the rifle was capable of mechanical MOA at 2km, steering it onto a man sized target is not difficult as long as the winds are steady or only mildly changing.
Smaller cals have an edge in pure short range accuracy (1000yds and in) by as much as 50% BUT become much harder to drive at extreme distances in the wind.
As an example, my 80gr Amax out of my 223 will make the trip to 1 mile with ease. In calm air, pretty accurate - call it MOAish. Add some gusts and for each MPH change, that bullet gets bounced 1min.
so a gusty 2 to 5MPH sidewind can move you 3 to 7ft if you don't catch it right. Throw in affects of tail and headwinds that can move you similar amounts and hitting a smallish object with this combo is tough.
You have taken a rifle with a mechanical accuracy of say 17" to a spray and pray device with a target zone maybe 7 to 14ft lateral, as much as 5mins of drop error - which force your bullet to land 10 to 30yds short OR long.
The head and tail winds have the same effect as dialing your scope 2 to 5mins up or down from where it is supposed to be. You got to be right on the ball with this rig.
By comparison, my 6.5 Mystic is easier to drive at 2km-2200yds
A BMG should drift about 50 to 70% less under the same conditions. So although the mechanical accuracy is similar/even worse, the drift zone is substantially smaller...
Like 1 to 2ft lateral and 1 to 2mins of drop error. If the winds were not bad that day, driving this type of ballistics is not that hard especially for a 'working' shooter. As he did, walking the shots on the target was a quick affair.
The big problem for him was likely spotting the conditions BEFORE sending that first shot. Otherwise, he would have been so far off the target that collateral damage a distinct possibility. Then he may not have seen the bullet impact and had no way of correcting.
However, once you see a puff, dialing in the wind is straightforward - didn't say easy.
With modern boomers, 1 mile is not very far away and a IPSC sized target is in great danger of getting smacked with only a sighter or two.
Jerry