Likely only by virtue of it sitting on Federal land (the District of Columbia). That is, if by the National Park designation you mean to imply a level of grandeur and majesty that the likes of Zion or Glacier National Parks bring.
To be fair, I've never been to Rock Creek Park, but photos of it make it look like any number of state- and municipal-level parks near me. :-)
I mean National Park in exactly the same way that everybody means National Park: Rock Creek Park was the third National Park, made so by an Act of Congress, just like any other big-N National big-P Park.
If you're willing to travel as much as it takes you to get to Big Sur from San Francisco, you can easily visit Shenandoah or the Blue Ridge, both bona-fide up-to-snuff pre-approved Real™ Beautiful™ National Parks from DC. There's also the Chesapeake, tons of magnificent beaches and state parks in the surrounding area---many beautiful sites on the east coast had already been state parks far before the notion of a national park was invented. That doesn't make them less beautiful or grandiose, however.
That's fair! I do acknowledge conceit in my comment, but you can attribute that to my jealously (as an eastern seaboarder) of the landscapes of the American West.
https://www.nps.gov/rocr/index.htm