If that's the tradeoff they're willing to make, who are you to say that they're doing it wrong?

Not every app needs 24/7 availability. The vast majority of websites out there will not suffer any serious consequences from a few hours of downtime (scheduled or otherwise) every now and then. If the cost savings outweigh the risk, it can be a perfectly reasonable business decision.

A more interesting question would be what kind of backup and recovery strategy they have, and which aspects of it (if any) they had to change when they moved to Hetzner.