You'll notice that only one of the top five is a Scandinavian.
You might not notice that all of the top five live in Scandinavia. Mamleev lives in Sweden. Omeltchenko lives in Sweden. Stevenson lives in Sweden. De Hass lives in Finland. Wingstedt lives in Norway. (Of course, serious elite orienteers must be spending a lot of time travelling around -- racing, training and visiting in other countries).
It isn't really a surprise that non-Scandinavian runners did so well in Hungary. The terrain looks fairly nuetral. It wasn't extreme in any way. Check out the men's middle distance course.
It isn't really a surprise that the non-Scandinavians all live in Scandinavia. For an orienteer, Scandinavia is the place to go.