FWIW, Raspberry Pi availability is starting to recover, and they do have the ability to boot off of a USB drive (including SSDs) or a network server these days.

FWIW, Raspberry Pi availability is starting to recover, and they do have the ability to boot off of a USB drive (including SSDs) or a network server these days. That said even SD cards are probably fine if you're not doing a ton of writes. (And it looked like a USB drive was attached to one of the PIs in the picture. So, presumably the important data is going there.) You're not wrong that second hand enterprise hardware would be more reliable but, honestly, I think this setup is fine for what they were trying to accomplish - especially if they already had some of the hardware laying around.