Another possibility:
Putin DID escalate to using Nukes, and Russia thought that missile had live warheads on it till it landed. Now they are simultaneously looking for the General that sold the warheads and trying to figure out how to spin this as a show of force.
Yeah, I thought about making that joke too.
If Putin launched nuke missiles expecting a nuclear blast, I think he'd have to ensure a nuclear blast occurred no matter what.
The US knew about the strike ahead of time and telegraphed that knowledge by closing the Embassy in Kiev because of a "significant airstrike" on November 20. So Russia knew that we knew, and if they were legitimately going to fire nukes and those nukes quite publicly did not go off, they would absolutely have to fire another missile and pretend the first one was decoys just to maintain deterrence. Putin has to have nukes to fall back on, and if he launches nukes and ends up with a lightshow, small craters, and a couple of injuries then there would be a perception that he has nothing at all backing his play.
The only reason why they wouldn't fire another ICBM or IRBM to make sure there was a nice mushroom cloud would be if they legitimately weren't confident they could make it go boom on round 2.
That said, the most obvious proof that this wasn't intended to be nuclear is that they wouldn't waste that many warheads on such a small area if they thought they were using nukes.
