Context is also helpful. “I’m not sure what’s novel about function composition” is a little bit of a smug take on a language and concept that was pretty cutting edge back in the early 80s. Now we Meat-and-Potatoes Programmers know the composition is useful, but I’d be hard pressed to find first-class composition in 1980 in any popular language that wasn’t {academic, Lisp}.

Well, it was 1983. So seeing something like this in a programming language was more novel than it is now.

Also, up to that point the author has only programmed in a couple of different assembly languages, plus Basic. Coming at it from that perspective, there's plenty of novelty to be found in Lisp family languages.

It was novel to you when you first saw it, which is what he's describing.

Not function composition, but higher-order functions.