You don't have to speculate, the article does state the method:

>> All modern mobile phones have a GPS receiver, which with the help of satellite can track the exact position of the phone with only a few meters distance.

>> The position data NRK acquired consisted of a table with four hundred million map coordinates from mobiles in Norway. A number in the table led us on the trail of Karl Bjarne Bernhardsen.

I think the general observation is that they (government, cell providers, 3rd parties to whom this is sold) have access to most GPS data and all cell tower triangulation data; the latter they have however often it is set up to be recorded.