It sounds more like there are a pair of systems where one operates as the primary and the other as a backup, and these can swap in case of problems with the pri

It sounds more like there are a pair of systems where one operates as the primary and the other as a backup, and these can swap in case of problems with the primary. That's fairly typical in critical infrastructure. I've done testing on these types of systems in the past (carefully) and the owners will often let you test against the system that's currently the "backup". So they probably restarted the "primary" after performing a fail-over.