I'm pretty sure that the swing/trend maps do not merely show the size of swings per se, but also show the impact of swings in changing the margin to a different "bracket" per election. In both the 2012 and 2016 POTUS elections, Finney County's margin was between 30 and 40 points Republican (Romney +39.0 in 2012, Trump +30.6 in 2016). However, Douglas county's margin was under 30 points in 2012 and over 30 points in 2016 (Obama +24.5 in 2012, Clinton +32.3 in 2016) Therefore, even though Finney's swing was larger, the swing in Douglas County moved the county from the "D +20-30%" column to the "D +30-40% column", whereas the swing in Finney did not move Finney from one "range"/"level" to another in such a way.
I don't think that's right. Looking at 2016 pres again, LA County had a larger swing than Monterey County. However, LA County's margin was in the 40-50 point range in both 2012 and 2016, while Monterey County's margin was under 40 points in 2012 and over 40 points in 2016. The swing map shows LA County in a darker shade of pink than Monterey County.