Re: War? Nope
They don't have to prove that Russia is at war with the USA, they need to prove that Russia is at war with Ukraine and that the damage caused by NP was collateral damage in that conflict which will probably be much easier to argue.
Opens up interesting legal arguments; collateral damage used to be easy to work out - 'was your chocolate factory close to where the bad guys were dropping bombs?' In a cyber war it could become - 'was your network connected to the same internet as everybody else's networks?'