It is interesting though to think about aftermath. If it is not an act of war, one can compromise a country's economy without going directly against the country itself.
I would counter that you don't need to violate all of the US's defense to bomb Hawaii and we all know how that was received. So yes, a state sending assets to go destroy some other state's property within the borders of said state is generally considered an act of war. That said, details matter a lot and these situations are basically handled on a case by case basis.
E.g. I’d argue that if China announced it would not repay its massive Treasury debts to the US, that would basically be an act of war even if no aggression was used, just due to the extreme destructive effects. And the reaction would be similarly upsetting, although not quite on the level of an unprovoked, large-scale military action.
But it quickly becomes a discussion of semantics at that point ;)
Other way round: US has “borrowed” money from China
An appropriate response needs to arise from a cooperative authority like the UN or Interpol, and needs a policy suited to address future events before they arise.
The US does this all the time and it is not labeled an act of war. The most famous incident is the Al-Shifa medical facility, but this is common practice in the "war on terror."
But dropping a bomb on a facility in Ukraine, with equally destructive shrapnel destroying facilities all over the world? Knowing that using this weapon can easily cause such collateral damage?
We barely have the terminology for discussing this type of warfare. The initial attack was an act of war, certainly. Beyond that, we have to come up with definitions and reactions. At the very least, it’s a subject for diplomatic channels, maybe even sanctions.