IIRC that's not how any of it went down. The authorities wanted access to the device itself and were asking for a "good guys only" backdoor into the device to obtain anything that might not have been in the iCloud backup; Apple refused to do this and that is where the controversy / news story came from.
Apple was very open about the fact that law enforcement would have access to the iCloud backup, which is even mentioned in the article you provided. And there was no "backdoor explicitly preserved" for the FBI, the iCloud backup was just not e2ee. This was also (somewhat) common knowledge at the time and what was often suggested was to do backups through iTunes because there was still an option available to encrypt the backup.
Apple was very open about the fact that law enforcement would have access to the iCloud backup, which is even mentioned in the article you provided. And there was no "backdoor explicitly preserved" for the FBI, the iCloud backup was just not e2ee. This was also (somewhat) common knowledge at the time and what was often suggested was to do backups through iTunes because there was still an option available to encrypt the backup.