It is not very clear from the writing but he analysed the QuakeWorld source. QuakeWorld is the internet optimised version. So this is for server and client having latency between them.
"I happily dove into Quake World source code."> QW is "Quake World" project, where Server and Client are meant to run on different machine (notice the client staring point is WinMain (in sys_win.c), whereas the Server stating point is main (also in sys_win.c)).