The reason new rifles in general shoot better is that manufacturing techniques have vastly improved due to the use of robotics and machinery. Also design tools such as cad and system modeling programs have refined the designs. Finally, there is more testing done today to figure out what works. This results in more consistent parts, assembly, and refinement.
Generally this should hold true and somtimes does but I will point out the purpose of the mas cnc machine was not for accuracy but rather to lower the skill level of the operator and cut costs...when the machine is working all is well...when the machine looses some tolerance or goes jawire in some way ther may not be the skill set to recognize it...you don't think they will back up a whole days production....they go out the door....
What CNC does allow though is the achievement of tolerances which used to take a skilled operator and often a good deal of hand work. That has meant that the sort of tolerances which used to be found on better (and more expensive) rifles have now trickled down to cheaper ones, because the cost of achieving these better tolerances is less.
It isn't just the barrels and receivers either. CNC machining has allowed such things as good inletting, bedding and even good quality checkering to trickle down.
As well as that, there are other technologies which have improved. There should for example be less excuse for off-specification work too, because such things as measurement technologies have improved, though as your example shows it is still possible for off-spec products to be made.
