@nullagent
It looks more like Ukraine attacked the naval base nearby and the Russian anti-air interception created the debris that struck the beach. I've seen claims that some russian aa missiles directly hit the beach, and not only bits of Ukrainian and Russian weapons.
In any case, this is hardly the first time there are civilian casualties in Russia due to Ukrainian fire. It's rather just another example that civilians always die in war even if you are careful, and not indicative of any new trend.