Lots of possibilities. I only go by what I see on the target, literally thousands of times and over and over again. IME, if I'm completely out of tune, the mean radius will be larger than my completely in tune mean radius, virtually, if not 100% of the time. Now, there are places in between, if I don't keep up with tune as conditions change, that may well defy that and agree with what he saw in his test. In a nutshell, just my experience now, but in tune shoots better than completely out of tune, by whatever means.
Maybe I'm misinterpreting something, as I often do. I'm not changing though. There's a method to my tuning process that tells me what I'm looking for and why. I've conveyed it on here several times and if you choose a different path that's fine too. There are different standards of accuracy for different games too. For me, a gun that won't shoot pretty consistent mid teens at 100 yards in good conditions, there's something wrong somewhere. But knowing that and having that level of accuracy allows me to trust what I'm seeing much more than if the gun was only capable of shooting say....300's on those good days. Is that the gun, the shooter, the conditions, the tune or what? I can't answer that for every gun and every shooter but it's my standard, regardless of competition discipline. Not talking hunting or even varmint rifles here, but what I know it takes to win at the highest level. I'll take a gun that will consistently shoot mid .1's with no big groups over a gun that shoots zero's when the stars all align just right. If you have a mid teen rifle, you'll statistically get a few zero's and a few .250's. But I wouldn't call either a surprise. Rather, it's what I'd expect. Who knows what it'd do in perfect conditions because I simply don't know anyone that shoots in a vacuum.