It’s often impossible to prove something didn’t happen. (Overused example: you beat your wife, prove you didn’t.) But when all parties involved universally denied the event (unusually strongly in this case), and the journalists couldn’t produce a single piece of solid evidence, especially considering the attack surface was pretty big (14 companies they say?), I’d say at least the story failed pretty epically as far as journalism goes.

Also take into account the fact that when the story first broke, people were quick to point to past reports by the same journalists that are provably false but never retracted.

Btw, last I heard about this story, it was said (IIRC) that Bloomberg assigned different journalists to re-investigate it. Did anything ever come of it?

It was denied. No one else was able to confirm the existence. Bloomberg never mentioned it again. Does not sound like a solid story.

How can you confirm that something is false without any evidence for it being true in the first place?