Contrary to Chris and Lauren's articles, this article from a Korean newspaper is stating that it is highly likely that it was a South Korean civilian defecting North!
This is what the Joint Chiefs of Staff Head of Operations Brig. General HWANG Jung Seon of the DPRK said in a press conference:
Considering how the holes in the fence were square-shaped and were opened South to North and footprints and handprints at the scene were imprinted from the South to the North, there were no particular signs related to an infiltration attempt, and it is judged that an unknown individual went to the North.Interesting contradiction from both sides. I am excited to see how this will play out.