>>An impressive fire in Moscow of an unknown cause...
Not surprising, given that central heat is out in several places. Even if people were trying to be safe (not using say, kerosine heaters - and I'm not at all sure those are a 'thing' in Moscow) just using electric heaters - in every apartment w/o heat is going to overload systems. I they're lucky, the wiring is good and the breakers pop. If they're not lucky...
In my area (New England, not as cold as Moscow, but not warm) residential electrical fires tend to happen in the winter.
TL;DR: probably not Ukranian (or partisan) action.