Why does reply all even exist on email? Crazy how in 2023 we are still relying on email etiquette a.k.a 'common sense' to prevent hugely disruptive interrupts like this. Can it even be disabled by admin?
What seemed to happen in the article is an email sent to a group-id (single email address that the server expands), not a list of a thousand-plus individual email addresses. To the client, a group email address is just an address---there's no indication that it will go to a few thousand people.