Double disk failure is improbable but not impossible.
The most impressive thing is that there seems to be no dataloss, almost whatsoever. Whatever the backup system is, it seems rock solid.
It's not even improbable if the disks are the same kind purchased at the same time.
I guess proper redundancy is having different brands of equipment also in some cases.
It's not always easy, but if you can, you want manufacturer diversity, batch diversity, maybe firmware version diversity[1], and power on time diversity. That adds a lot of variables if you need to track down issues though.
[1] you don't want to have versions with known issues that affect you, but it's helpful to have different versions to diagnose unknown issues.
https://www.neoseeker.com/news/18098-64gb-crucial-m4s-crashi...