I'm not so sure that this Norwegian farmer understands that with one quick look. I translate that into soil quality is the ability of the soil to do what you want it to do. Soils of good quality are healthy soils. A spoon full of healthy soil may contain more micro-organisms than there are people on earth. The greater the biological activity of a soil the more productive it is.
Earthworms have a great effect on the soil.
They are a good indicator of soil quality. Many earthworms in the soil indicate a high quality soil. After zero-tilling for sometime, I noticed my soils developing more structure. The soil was becoming porous, less compacted, much more mellow. Then earthworms started showing up, in great numbers over the years of no-till.