The article mentions yoga classes held on the National Mall, and the DC Global Mala Project.
The other “Fantastically Yoga Friendly Towns” are Asheville, NC; Austin, TX; Boulder, CO; Encinitas, CA; Minneapolis, MN; Portland, OR; Salt Lake City; New Orleans; and Woodstock, NY.
It's so great to see DC mentioned among all these “hippie” cities! It's a welcome observation, as most of the country likely views DC as a buttoned up, serious town. However, once you move beyond the tourist spots on the National Mall downtown – yoga studios abound; especially in Woodley Park, Adams Morgan and Dupont Circle yoga mat toting locals are plentiful.