Thinking too concretely about monads as boxes might make the behavior of the ListT monad transformer seem a bit surprising... unless you were already imagining your box as containing Schrodinger's cat.

I can definitely understand the author taking offense to the interaction, but now that a lot more programmers have had some experience with types like Result<T> and Promise<T> in whatever their other favorite typed language with generics is, the box/container metaphors are probably less helpful for those people than just relating the typeclasses to interfaces, and pointing out that algebraic laws are useful for limiting the leakiness of abstractions.