I still recall how to build a Linux system from go. Coding what you're working on up in Python/C would take a large unrelated amount of knowledge.
The first version of the program used a simple UDP broadcasting method to a hard-coded port to find servers, which required some rudimentary networking knowledge, but only basic TCP/IP stuff.
Later, both the server and client parts have gone through numerous refactorings which brought in many features (like a plugin system on the client side, and a D-Bus interface on the server side), but those were manageable chunks to add to an already mature and working system.
But sure, in addition to the knowledge one could acquire from LFS, I also had some high-level knowledge of how TLS and its handshake worked, I knew that there was some way to use OpenPGP keys instead of X.509 certificates in TLS, and I knew a little about how DNS-SD worked. The rest I needed I read up on as I wrote the code.