Sigh, sounds very familiar, like what people say about Mandarin and Cantonese, those who don't know.
This is a different hack, but I think they more reliably differentiated between North Korea and South Korea, due to the IP addresses?
"Korea seeks U.S. help in reactor hacking probe"
http://m.koreaherald.com/view.php?ud=20141222001202&ntn=0
From what I've seen in the South Korean media, no one is talking about North Korean involvement in this separate hacking incident of nuclear reactors. The codes seem to be different from those used in previous attacks blamed on North Korea.
Note that linguistic evidence doesn't come into this, just as one wouldn't usually be speculating about which English-speaking country a hacker was from simply based on the code.
This is a different hack, but I think they more reliably differentiated between North Korea and South Korea, due to the IP addresses? "Korea seeks U.S. help in reactor hacking probe" http://m.koreaherald.com/view.php?ud=20141222001202&ntn=0