Most of the account sounds overblown (and specially crafted in the model of 1984, Nazi camps and such).

Any corroboration for this story? Because "escaped" people are known to say anything, especially since it can be very profitable outside their country.

For one, people like and buys survival stories (the harder the better), second, if they are nicely crafted they can serve as diplomatic pressure and propaganda (which is not the sole province of North Korea).

So, any actual evidence, outside what just one man says that we are supposed to take for granted?