That seems accurate in my experience.
I mean, not knocking who told you that at all, I think it's funny that they applied it to Medium the website. Just a little tidbit of info about the quote's origins, in case you weren't aware!
Given the nature of the medium, books usually have the highest guarantee of quality due to the resources used to publish a book.
I won't try to guess why, but the few pages I can access are always high quality, while poor quality pages (as discovered when opening the page anyway in a full browser) always try to block that setup.
I suspect quality means different things to different people and even changes based on context for the same person.
For instance, a blog describing some arcane linux command to run to fix the issue you're having does not need to be the same level of quality as something you're reading to learn + get in depth info about a topic you know at a very shallow level.
Usually you can find the signal in the first 2 or 3 sentences of in any post.
Medium.com has better SEO than SO and small personal blogs, so it's winning when searching for a solution.
At any rate, the idea is to somehow filter out all the garbage when I just want to know how to do something. Too often I have to find personal blog links on stackoverflow ("PS. I wrote more about it here") as opposed to that helpful article simply showing up in the search results by itself.
It would be interesting to see a curated version with an allowlist of domains as well, like how Angelfire and friends in the 90s used to be with a "web ring" of peer websites.
I have found several articles about Apache Kafka on Medium that have helped me a lot. I have no idea if it's by a junior dev or not.
I don't think they geniunely want to help people learn. I assume, given the low quality / effort content, that most are just trying to use them to build a prescence to help get jobs?