I saw this video too today and thought; probably some very custom electronics & software, where only the mechanical 'keyboard' is the same. Doesn't matter though, it's a pretty cool thing to behold.
Standard keyboard = 104 keys
x 16-bit RGB = 208 bytes
160 keyboards
30fps
-> roughly 1MB/s data rate
Little need for header for USB or ethernet protocols. You could just send new frame data and use a frame sync packet to latch the data to the display.
160 devices could go over 2 separate USB hosts (which is present on most PCs anyway), but probably not deterministic enough for frame sync.
A simple UDP protocol that transmits 1 multicast/broadcast packet as a frame synchronization is easier. However, UDP is not exactly high QoS, so it could even be a mix of UDP and TCP.
Makes me wonder though, why it couldn't be done at 60fps. Because after all, that is what the whole
PCMR reddit (and thus most PC fanatics) is all about.