I don’t think we disagree too much here. Note at the top of the post we say that none of these categories are per se bad, just that the absence of them doesn’t mean too much. Open source can absolutely be a great place to develop skills; I taught myself PHP hacking on WordPress way back in the day, for example. It is also clear that many open source communities organise and communicate in a way that is off-putting to lots of people.
I personally know a bunch of great engineers who stopped contributing to open source projects because of cultural issues. I also have excellent colleagues who have never contributed. Medium still has an exceptionally strong culture of sharing and learning. Fully one third of our criteria for judging candidates focus on this!
Recognition that some open source communities are unwelcoming says nothing about Medium’s contributions to open source in general. We’ve released quite a few projects under open source licenses, and have submitted reports and patches to other projects, both independently and in our capacity as company employees, mostly on browser-related issues (including the Chromium project!). Medium engineers have made substantial open source code contributions at places like Mozilla, WordPress and Google, and many continue to do so. We released our hiring documentation under open licenses to encourage modification and reuse. We’re not as active as, say, Facebook or Twitter, but then again, there’s less than fifty of us in engineering here (and that with a bunch of recent hires).
Not all open source communities have these kinds of problems, but many do, which is why we don’t judge people for their decision not to participate.