A missile cruiser is going to have a lot of hypergolics on board. If you don’t know what you’re doing that’s an easy way to blow yourself up, like what happened with the submarine Kursk.

So it’s plausible that it wasn’t the Ukrainians, but then again it would surely be more honourable to get blown up by a Ukrainian missile than by your own incompetence. So if Ukraine is falsely claiming credit they should be taking it as a propaganda godsend.