I personally think it might have launched an S-300 SAM whose main rocket motor might have failed to fire and it dropped back onto the deck and burned and started an internal fire that the fire fighting equipment on board was unable to deal with.
HMG mounts and just sailors with small arms can put up a lot of tracer ammo to scare away manned speed boats or attack aircraft, or just hit and destroy small surface targets like floating mines or surface drones.
There was even talk of using supercavitating rounds from the 30mm gatlings to shoot into the water a few metres deep to destroy incoming enemy torpedoes.
Older ships the size of Moskva have enormous potential for carrying and operating their own drones too... there is no reason to say a drone swarm can't be dealt with using large calibre HE rounds like a 152mm airburst round set to explode amongst the enemy swarm, and of course your own drones going out to knock enemy drones down too.
Even EMP shells could be used, and of course on a large ship there is space and power and cooling potential for lasers and radar jammers... a drone swarm rendered blind is not effective either.