There is little doubt that the article is a continuation of the well-known long-standing debate about proofs of correctness in programming, program verification, theoretical precision, formalism and related topics.
Dijkstra was a big life-long proponent this approach. See Hoare's memorial lecture (2010).
This is discursively placed in opposition to practical software engineering, applied computer science, where proofs might be replaced with testing.
Early on it was held that large programs could never work because the amount of errors would be unmanageable, hence the only rescue is to formally prove correctness for software to work at scale. Early on Hoare advocated that position, but he later changed his mind (after Dijkstra's article in question see Hoare (1996), and in fact other computer scientists further argued that it is neither practical to prove everything, while arguing that it has borne out that large programs actually do work without being fully formally proven.
A paper by DeMillo, Lipton, and Perlis (1979) is probably the most famous example of that argument. Dijkstra not only disagreed but disagreed with quite some vehemence. (For some more current comments by DeMillo and Lipton and others see Gasarch (2021).
The article in question is ten years later, now even larger software systems are in use, while not proven correct, yet Dijkstra advocates for the formal, highly theoretic, and proof-centric approach in pedagogy. Dijkstra knows this is controversial, and the commentaries by his peers confirms this. They do know Dijkstra and his position as well. I believe there is a decent chance that mention of cruelty are as much if not more directed at his peers as the imagined CS student. And the wording of "really teaching" is a dig at his peers doing it wrong, according to Dijkstra. Dijkstra is a highly esteemed computer scientist and Turing award winner. But it's noteworthy that the same or similar can be said about numerous of his respondents. So he is really arguing that colleagues at premiere computer science programs such as Berkeley, Stanford, CMU and others are not teaching CS correctly. It's easily understandable that this is a way to have that kind of a discussion that leads to controversy.
See for example this paragraph from Dijkstra's argument:
In the same vein, I must draw attention to the astonishing readiness
with which the suggestion has been accepted that the pains of software
production are largely due to a lack of appropriate “programming
tools.” (The telling “programmer’s workbench” was soon to follow.)
Again, the shallowness of the underlying analogy is worthy of the
Middle Ages. Confrontations with insipid “tools” of the
“algorithm-animation” variety has not mellowed my judgement; on the
contrary, it has confirmed my initial suspicion that we are
primarily dealing with yet another dimension of the snake-oil
business.
