From the follow-up article: https://rachelbythebay.com/w/2022/01/27/scale/

"If you are sticking with the 2022 equivalent of MS-DOS and machines that do exactly one thing at a time, then yeah, you are going to have a whole fleet of systems all sitting there busy-waiting on something stupid."

"Don't recreate the basement full of PCs when the problem can actually be solved with a single box sitting in a cabinet somewhere."

If they really were just PCs to act as a modem-to-network bridge, this seems to be remarkably cost-inefficient. I remember around 1997 helping the university chuck out a few serial line concentrators (no idea what they were actually called), each of which had 32x RS-232 ports that worked up to 19200 baud and a 10Mbit coax network connection at the back. The on-board computer (wouldn't be at all surprised if it was much more than a 68000 or two) interfaced with all the serial ports and translated it to telnet on a remote machine. You could also send it an escape code and then via a primitive command line connect to any arbitrary IP address and port over TCP. I remember in my student days (so maybe 1995) using finger and SMTP directly from these text terminals without actually logging on.

No idea when these became available, but we were chucking them out in 1997 or 1998 as we were upgrading the labs of text terminals to PCs, so they probably at least a decade old by then.