A tolerance of 1/8 millimeter (5 mils) can certainly be achieved by CNC machining, but not always by the cheapest tools.
You mean that it is easy to achieve much smaller tolerances than this by CNC machining?
Googling for "CNC machining tolerances" finds at first hit a guide that says "For CNC machining, the standard tolerance limit is set around +/-.005” (0.127 mm)."
The next hits show the same 5 mils standard tolerance, but they also mention the availability of better tolerances, like 2 mils or even less, but at higher costs and subject to various constraints on the features to which they are applicable.
So it appears that the tolerance written in the article is indeed typical, as claimed.