As an electrical engineer that works in critical facilities, I have to say that this is a big failure. A switchgear failure is not an excuse. There should be auto-transfer switches, UPS units, emergency generators, etc. that keep critical equipment online.

My guess - poor maintenance of electrical systems. Which is kinda surprising for someone as regulated as an airline, but then again, this is back-end stuff and not planes in the air. If your systems aren't tested, when something actually happens, you are not going to get the result you intended. My guess - primary power failure was followed by failure of a transfer switch, or batteries, or generator, etc.