My guess on root cause: They did not actually test restore from backups.
So most likely nothing new under the sun.
Root cause - guardrails "unexpectedly" were neither guards nor rails. Who knew that asking a stochastic program "pretty please" is not a strict instruction or a barrier whatsoever.
Bet there was an executive telling we cannot afford old-time security in the era of AI. If they had guardrails outside of the prompt they were getting left behind.
Easy: non working backup system in place.
This would have happened if some disgruntled employee deleted everything.