That map is confusing, regions are colored grey that are clearly in the top 20 MSA, like the entire urbanized northeast. Also the article's mostly about Nashville, not its title.
It's not the 20 MSAs with the most jobs, it's the 20 MSAs with the most job growth, as a percentage, since 1990.
From the article>>"...40% of the new jobs generated during that time went to the top 20 places, along with a similar share of the additional wages. Those cities represent only about a quarter of the country’s population and are concentrated in the fast-growing southern and coastal states. None were in the northeast, and only two were in the “rust belt” interior - Grand Rapids, Michigan, and a rebounding Detroit."
New York City is the capital of Norther American commerce and because of that it really can't expand the way that <mid-tier former manufacturing city anywhere else in the country> can, which weakens the overall point about "slow growth" or "getting left behind". Growth doesn't mean the same thing everywhere.