So basically functions vs objects that provide methods that operate on opaque data types, except this was written at a time when programming languages that offered modules, such as Modula-2, had yet to appear, although one could then, as now, implement them yourself in C.

To modern ears, the title of the article seems to falsely promise that it's about system design - criteria for decomposing a system into modules rather than on the benefit of information-hiding modules over collections of functions.