Regardless of how old is this video, the idea of a successful nuclear attack on US soil is greatly desired by many, from individuals to states. The sentiment and threat are taken seriously, not just by US but by many countries, allies with US or not. Even the simpler functional nuclear explosive device, a 'dirty bomb' aka radiological weapon, is beyond the technical scope of non-state organizations like al-Qaeda so that leave some measure of state sponsorship from one or more.
NTI: Global Security Newswire - D.P.R.K. Test Spurs U.S. to Discuss Nuclear Attribution
Nuclear attribution is part of nuclear forensics and even though the program is not available for public analysis and opinions, the US is the world's leader in nuclear forensics and nuclear attribution teams ready to move. We will find to a great degree of precision on who was the supporting state.