Re: backup systems
The description here is slightly ambiguous, but I think what they mean was, the backup system was physically distinct but not logically distinct. It was specced to be the exact same system but running on a different server box, so that in the event a Hardware failure took out System A, System B could immediately step in and take over, because it's "the same system" just on a different box. But in this case the hardware was fine, and a software failure took out System A, and when System B tried to step in...it immediately suffered the same software failure, exactly because it's "the same system" running the same actions.
(Really "software failure" here means "design failure that triggered a software failure when faced with hardware limitations", but that's too wordy and gets us to the same result anyway.)