Either they have huge noggins or they are very small.
North Koreans in general are very undernourished, and have been for years. The Army tends to get good rations compared to the rest of the populace, so if these are the best specimens, you get an idea of how bad it is.
Because of successive famines in North Korea since the 1980s, the average fully grown North Korean male is significantly shorter and lighter than his average South Korean counterpart. The only compensation is that once they join the army, they are then better fed than the average North Korean.