Reading the underlying study, one of the most important factors is "Monthly Average Inches of Precipitation" and "Yearly Average Percentage of Sunshine"

Through they also apparently think that Fullerton CA have the best walkscore in the country, so garbage in, garbage out. Actually, I figured out how that works too. Walk score, the organization, have an average for each city. Many smaller cities are too small to get a score from walk score, so this group just took a central point in the city and used that as a walk score. So yeah, they are gonna do well in the study and like shit in real life.