Researchers examined the median home prices last year for roughly 575 U.S. counties and found that home prices in 99% of those areas are beyond the reach of the average income earner, who makes $71,214 a year, according to ATTOM.

This sounds like they compared the national mean income to local median home prices which honestly probably makes 99% too generous, it's probably closer to 100% unless the article is explaining what they did poorly.

The lowest cost of living areas are going to be the ones where these houses are most affordable but they're also lower income areas normally and a normal person isn't pulling 71k a year in middle of nowhere Tennessee or whatever.