Someone mentioned before that the Moskva's radar system had not been modernized and could only engage a single target. I doubt that. It probably could engage a few targets simultaneously. The Ukraine side probably used a few UAVs to distract the cruiser. I'm wondering how many targets can China's 055 with its modern AESA radar engage at the same time? Hundreds?
I am more the side that its sheer snafu given the Russian Navy's horrific safety record, where we have seen ships repeatedly that suddenly go on fire, and nearly go kaboom. The latest incident was an advanced corvette under construction and this one happened a few months ago. Given the state of the Moskva, which is in a very poor state --- halfway to a scrapyard is the best way to describe it --- its much more likely it is an accident. If Ukraine has active antiship missiles, why fire it on junk, when they should have been fired on the modern corvettes and frigates in the first place, which should have been done in the beginning of hostilities, before these ships would repeatedly and repeatedly unload one Kalibr salvo one after another against your precious ammunition stores, fuel bunkers, vital railway depots, and personnel concentrations.
Assuming the Moskva's weapons systems are running, which I don't think it was, the Top Dome phase array fire control radar would have been capable of multiple engagement, but only in the quadrant direction the FCR is turned in. This radar sits on a pedestal, which is turned around in 360 degrees. You can potentially distract the Top Dome with a decoy in one quadrant, while the antiship missile comes in another quadrant, but that kind of coordination seems rather effy. Furthermore the two functioning search radars would still have picked up the antiship missile. Even if the ship is not upgraded with Top Plate, the older Top Pair or Top Sail or whatever you call it, you can see the two search radars here, are still back to back arrays. That's not just one, but two of them. Finally, the Kashtan CIWS also has its own radar.
Another possibility is that the ship is sabotaged by someone who is intensely dissatisfied of either the Russian Navy or the current Putin regime, and it can be done as simply as arson. We know of the recent case of the Bonhomme Richards for one.