Well the NK people have said they are developing a space program. As you stated, 1200KM altitude is what you
want if your goal is an ICBM. Aiming for
double that sounds more like development of an orbital deployment system than an ICBM.
http://www.abc.net.au/news/2017-05-14/north-korea-fires-unidentified-projectile-south-korean-military/8524684They would have gotten much more useful data if they'd stuck to a normal trajectory, so that sort of raises questions of why they'd deploy this expensive rocket test on some trajectory that isn't going to furnish them with good data about ICBM design, if this is in fact an ICBM prototype.
The west has a record here, at least three times (1998, 2009, 2013) NK has launched an orbital test and each time SK and USA claimed it was a veiled ballistic missile test, but later retracted the claims when the device was shown to have followed an orbital trajectory.
https://en.wikipedia.org/wiki/Korean_Committee_of_Space_TechnologyThe DPRK twice announced that it launched satellites: Kwangmyŏngsŏng-1 on August 31, 1998 and Kwangmyŏngsŏng-2 on April 5, 2009. The USA and South Korea predicted that the launches would in actuality be military ballistic missile tests, but later confirmed that they had followed orbital launch trajectories.
https://en.wikipedia.org/wiki/Kwangmy%C5%8Fngs%C5%8Fng-3Kwangmyŏngsŏng-3 (Chosŏn'gŭl: 광명성 3호; Hancha: 光明星3號; English: Bright Star-3[2] or Lode Star-3[3]) was a North Korean Earth observation satellite, which according to the DPRK was for weather forecast purposes, and whose launch was widely portrayed in the West to be a veiled ballistic missile test.
It's sort of a repeating pattern, NK does do something actually to do with space, the western media claims it's a sham, but later admits the space-related thing actually does exist. NK is a basket case but that doesn't mean that you should trust your own side when they write up about NK.