To be clear: I didn't make the hardware or the Lisp implementation -- those are from http://makerlisp.com (which is not me). I just made the game and plugged it into telnet.
The hardware does actually support acting as a serial terminal over USB, so I considered trying to plumb something up that would connect the telnet connection to the actual hardware's terminal so you could be playing across the internet on the actual hardware, but that was just too fiddly to do in the time I had, and it would have meant only one person could play at a time (and meant I can't use the machine myself!).