DPRK Stealth Vessel
Media outlets around the world reported on the "official" recognition of the craft, however there's definitely more than one.
The vessel, which is similar to a hovercraft (something the North Koreans seem to be fixated on), features an angled hull and other features which help to scatter radar. You'll note the similarities in design between the small North Korean ship and the British HMS Daring destroyer seen here:
British HMS Daring
These "surface effect ships" use hovercraft technology to reach high speeds without the need to decrease the weight of needed weaponry.
North Korea has been trying to modernize its military for two decades, but change comes slow to an overly bureaucratic nation severely low on funds.
The specific ship reported on has been known since 2009, when it was visible on satellite imagery of the Munchon Naval Base (11 miles north of Wonsan).
Ship onshore in Munchon, 2009.
However, after reviewing images from Wonsan (and comparing image dates), North Korea has at least two of these vessels. Both ships can be seen in their respective docks on images dated 10/3/2009.
The Wonsan ship can actually be seen on images dating as far back as 2002.