we can't assume anything from one response! We can only say that we don't know - when shots have been fired at or on the Zaporizhzhia nuclear base, it's sensible to start from the assumption that it was Ukraine's fault.
The Zaporizhzhia nuclear base has been taken over by the Russian military who are using it as a base. Ergo the Russians wouldn't be stupid enough to shell their own military base, especially considering the fact that the base has nuclear stuff in it.
It must be Ukrainian fighters who fired on the base.