Don't use a sports-car to haul furniture or a garbage truck as an ambulance. For the use case and scale mentioned in the article it's obvious not to use a database.

Am I missing something? I guess many people are the using the tools they are familiar with and rarely question whether they are really applicable. Is that the message?

I think a more interesting question is whether you will need a single source of truth. If you don't you can scale on many small data sets without a database.

I will say this before I shut up with my rant: If you start with a design that scales you will have an easier to scale when it is time without re-engineering your stack. Whether you think you will need to scale depends on your projected growth and the nature of your problem (do you need a single source of truth, etc.)

Edits: Spelling

Even it's postgres, it is still a file on disk. If there is need something like like partitioning the data, it is much more easier to write the code that partitions the data.

If there is a need to adding something with textinputs, checkboxes etc, database with their admin tools may be a good thing. If the data is something that imported exported etc, database may be a good thing too. But still I don't believe such cases, in my ten something years of software development career, something like that never happened.