That is also my current working hypothesis. Iran pays Russia to deliver to N. Korea technical help in terms of sample components and missile design consulting. N. Korea successfully produce nuclear-tipped missiles and the N. Koreans will help developing the Iranian version of the same model. The entire loop is complete: Iran - Russia - N. Korea - Iran.
Russia is probably paid handsomely by Iran. The money Obama gave to Iran can do some wonders.
A solid fuel, road mobile ICBM with a 150kt thermonuclear warhead is no small achievement.
It took the US and Russia 30 years to get to that point (start point 1950).
Yes, we know the Norklandians did not get there in 20 years without help. It’s inconceivable.