Yes, of course, when working on a piece of code (a low-level task), one should know where it sits within the bigger system. One needs to know all kinds of things about what lives both upstream and downstream, as well as some high-level architecture of the system as a whole. But the implication above (which I disagreed with) was that "good coding skills" (and thus a filter during hiring) implied "good documentation skills" does not follow from any of that.

Again: Code is always "low-level" (regardless of how much you do or don't know about the rest of the system) just like most API documentation. The complaint of the original article wasn't about API documentation, but about higher-level conceptual documentation being lacking. And just like not all "coders" may be able to design a large and complex system (though they may certainly be able to understand it) they also may be unable to document those high-level conceptual aspects of the system.