If one stops to think about the odds of such micro groups occuring compared to what the best benchrest rifles and shooters produce on average, such "unbreakable" records will be eventually shattered. After all, the groups are all zero at the muzzle, aren't they?
Such groups are mostly luck, in my opinion, otherwise they would be commonplace. They happen about as often as the largest group fired by the rifle and shooter producing the record smallest one. All the other groups' sizes are between those extremes. Having once put 5 shots into about an inch at 1000 yard using aperture sights slung up in prone, there's no way I would claim that any sort of accuracy excellence; it was pure luck as the shots were not called that close together.
But it's nice to see it happen.
Regarding the ability to measure them, there are special gauges used to do so and can easily discriminate fractions of one thousandth inch through magnifying glasses. Here's an example of one:
http://bulletin.accurateshooter.com/...il-jones-tool/