The problem statement is basically copied verbatim from RFC 5246 sections 5 and 6.3.
The author picked a cryptographic function from a rather important and widely deployed real-world internet protocol (TLS 1.2), but of course since the author is writing about Haskell readers assume it must be some esoteric academic nonsense that undoubtedly involves category theory, whatever that is.
I didn't say anything about "esoteric academic nonsense." Just because the subject matter is a part of something that is very commonly used does not mean it is outside the reach of many very competent people.
The author picked a cryptographic function from a rather important and widely deployed real-world internet protocol (TLS 1.2), but of course since the author is writing about Haskell readers assume it must be some esoteric academic nonsense that undoubtedly involves category theory, whatever that is.