The article is about the hardware and kernel level APIs used for interacting with storage. Everything else is by necessity built on top of that interface.
"fopen"? That is outdated stuff from a shitty ecosystem, and how do you think it's implemented?
its not a real problem for most modern developers.
pwrite? wtf?
not one mention of fopen.
granted some of the fine detail discussion is interesting, but it doesn't make practical sense since about 1990.