First, there is no proof of the original claim, other than words of Ukrainian mayor.
Second, this explanation is much more logical than the version with russians firing superexpensive anti air weapons to random ground targets.
Third, there were photos of these missiles, and they belong to older series of rockets. Russia dismissed these old s-300 long ago, but Ukraine have plenty of them.
https://www.thedrive.com/the-war-zone/russia-now-firing-s-30...