Do we even know if it works anything like that or its just an assumption based on the half-assed american project?
No one knows for sure but the general principle points in that direction. If the Russians have revolutionised miniature reactors in some other fashion, working on much better principles for creating thrust, then they would be expanding it to many things and many fields. So it's a pretty decent assumption from anzha. The technology itself is still super impressive to manage in a cruise missile sized vehicle. The Americans didn't really complete Pluto, although little doubt they could if they really wanted to. It is simply less useful for the Americans like an assault rifle isn't a suitable tool for a wealthy man walking into a bank to make a deposit. It's also why the US never really bothered that much to finish developing HGVs... they simply had less need for one because of the types of wars they want to fight and how they want to fight them. However HGVs are perfect weapons for nations defending against CBG main assault forces and regional military bases littered around you.