the title of his blog"Facebook's software architecture" is misleading.
actually these papers are talking about data storage and database. not "software architecture."
Though, his blog is informative and consistent. Love it!
Digital data and information storage is not a component of a software architecture? Of course it is, and anyone working on a similar project would need to include these layers in their architectural specifications.
One could argue that software architecture is the inner structure of an application, i.e. the libraries, modules, classes, functions and, most importantly, their interfaces. The GOF design patterns are purely a matter of software architecture, for example.
System architecture on the other hand describes the different applications/services that compromise a system, including the ones that you write yourself, plus the ones that you just "use", e.g. database, storage, load balancer, etc.
I would argue that the article mostly talks about system architecture with focus on storage and I guess the parent you replied to would too.
I was Dr.Demirbas's student. So pleased to see his article on HN front page. Such a great memory in his class and seminar. Back in days, he held a course called distributed system seminar. In one semester, we read and discussed 28 distributed system related papers. This gave me a whole new level sense of this interesting field. Thanks Murat.