Because not all government funding is federal funding.
Random example from an NPR member station's web site:
KCRW is supported, in part, by the Los Angeles County Board of Supervisors through the Los Angeles County Department of Arts & Culture. The Department's Organizational Grant Program helps fund a wide variety of arts, culture, and music programs that you hear on air each day!
I apologize for my imprecise language. The 13% I quoted includes "Federal, state and local governments". Again this is all on the web page we're all discussing, in a very easy-to-understand chart.
Random example from an NPR member station's web site: