That's my opinion too.
These projects are secret, the Russian developers and politicians misinformed the other countries about them just like Nato does with wrong goals, designs, figures, and mixing up project natures and names.
The people who described the accident to the Press lied as part of their duty and they probably understood little about technology. The reporters understand zilch usually, mix up the information, and put anything in their paper. "Experts" and "senior analysts" just say anything random.
What elements of information are credible in this context? Maybe the explosion, the deaths and injuries, the small spike in radioactivity, very little more. Good luck to infer anything from that.
Source related with the project spoke of "liquid propulsion" and "isotope power source" if the translation is accurate. In Western media it became "missile" and "nuclear reactor", even "Burevestnik".
I strongly doubt the tested thingy was a missile.