The author does not provide a methodology so it is hard to say how he arrived at his conclusions. At the same time the results appear reasonable for a number of states (and cities in CA as the there is city data for CA). Maybe worth a minute or two to review.
My comments are based on direct experience in a few of the states listed as both a landlord or homeowner over 20 or so years. Nothing more than seat of the pants from my side as I would need to know more than what was presented to really comment.
See MarketRisk’s entry (including graphs)