I found the article to be terrible, and his school building analogy falls flat on its ass. Both junior and senior developers can and should contribute to open source, for a variety of good reasons and there are good ways to go on about it.
If you could clone a school essentially for free, and also a poorly constructed school was not at risk of killing a bunch of kids, I guess we’d be much less skeptical of amateurs building schools.
I do think people write programs best when they are the primary audience, so the idea of just, like, going around with the explicit intent of finding open source projects to contribute to seems a bit misguided. But the stakes are not very high. If nothing else I imagine most open source projects must be able to ignore non-useful contributions, right?
The problem is when someone wants to contribute primarily because they think it will be good for their resume, or even just for a more amorphous "I feel like I should give back" type reason. These sorts of motivations often result in contributions that end up being a drag on a maintainer's time, with little upside. People coming at it from this angle usually don't become dedicated contributors who grow and improve over time. They become a time and energy sink.
I've unfortunately witnessed this firsthand many times in my 20+ years of open source involvement.
Edit: Changed author to contributor as it can be confused as the author of the article.