Thats pretty dismissive of the point of the article which focuses on quickly synthesizing their own interpretation in notes, setting up systems for spaced repetition, and filtering what books to even use this system on (by skimming free samples online before purchasing).

It's not about memorizing useless information, but about how to remember all the ideas you've learned so you can actually use them later. Especially if you're learning a lot all the time

I guess that depend on whether those digits were meaningful information to them or not. Because if they're "just digits", then there's nothing to remember.

No, it doesn't. The point is to remember what you want to remember, not to memorize the whole library.