Didn't realize there was a reply.....
Lol it's not written by AI, the guy has videos explaining the project and he's made posts in the LinuxCNC forum. No idea what the issue with the github page is, it looks fine to me....at least he took the effort for something open source.
There's nothing else to use, it's targeted at communication with LinuxCNC, it's not general Arduino firmware.
The LED cathode lines being shared with the key column lines is specifically the point, it's meant to save IO lines (16 vs 64). There was some discussion about this on the LinuxCNC forum with the author and someone did get it to work with an OEM keypanel shown in that paper schematic I posted but it's largely untested, even by the author as he didn't have the hardware to test. The author's gone quiet or I'd ask him about it. I'm making my own LED/keypanel so I can make whatever changes are necessary. I'm just not totally familiar with the concept of this type of matrix/mux so I figured this the best place to ask.