OSS activity is a useful low-effort implicator. As usual for implications, denying the antecedent remains a fallacy.
That is an assumption made without evidence. An equally qualified assumption would be that its a sign of privilege to not need to contribute to open source. You get an awesome education and go straight into well paying entry level position.
Committing to open source is not something casually done at ones leisure. Anything with traction becomes a significant responsibility and it takes an incredible amount of discipline and sacrifice to stay committed.
I think it's better to consider privilege as multifaceted rather than a single global quantity. And in that case, I don't see such a strong disagreement between you and the comment you're replying to.
I very much agree with your second paragraph.
Or maybe there are both friendly and unfriendly projects and a lot depends on where the underprivileged is trying to make it.
You're constructing the viewpoint you want others to see with no data or facts to back it up.