There are multiple contexts at play here. It’s ambiguous, and multiple parties want to keep it that way for their own reasons.

Russia/China/US would I’m sure like to keep plausible deniability here, as it minimizes outright repercussions (for everyone), while still keeping the option on the table for them to tit-for-tat.

It wouldn’t surprise me if any insurance involved (which surely wouldn’t pay out in event of war) would want to claim it was an act of war.

Anyone trying to claim against such insurance would want to claim it wasn’t an act of war (just a mistake), so they could get the payout.