9/11 was presumably intended to damage as much property and kill as many people as possible. So no, the people who died as a result of that terrorist attack against the US were not killed by accident.

Yes, if your gun accidentally goes off during a robbery, that is by definition an accident. An accident that could have been avoided if different choices had been made, but still an accident.

If the intended target in this case was the Ukraine, and companies in the USA suffered immense damages it's reasonable to ask if those unintended consequences were accidental. Similar to how a bomb dropped on an Italian border in WWII might accidentally kill ally French citizens on the other side of the border. With cyber warfare it becomes much more interesting, because those accidents don't respect physical distance.

I kind of feel, and I'm not going to pretend I'm an expert, that digital warfare should be treated closer to biological warfare than just your typical bombs and bullets kind. Generally, and holy shit I know someone is going to flip their shit for me saying this, but generally a regular bomb (not nuke) is an acute type of problem. After it goes off, it's GENERALLY harmless after that. Yes, structure collapse, contamination, gas leaks and other after effects. But not really more booms from the bomb. Weaponized ebloa can still make more people sick, not affected by the original release. Same with NotPetya and other cyber attacks. After deployed, it can affect more and more targets as time goes on.