I think the author is attempting to make the very valid point that not all good programmers can be expected to be giving freely of their non-work day time.
In short -- life happens but then the jobs dry up and good talent is over looked or lost.
I don't think even companies that "require" a strong GitHub portfolio are saying that they're not filtering out good or great programmers. It's about signal and noise.
If you are hiring for a senior development position and you have a filter you can employ that will cut out 90% of mediocre or bad programmers (or perhaps more importantly make it much easier to identify them), but will also cut out 40% of good and great programmers, it's not a foregone conclusion that you shouldn't employe that filter. If you still get enough resumes to make a decision, you've just decreased the odds that you get a shit hire by $MATH percent.
If social justice is something you care about you probably don't want to do this. If building good software is something you care about, you probably do. I think most here would agree that a random developer with a large body of public OSS contributions is probably "better" than a random developer without. I say that as someone who has pushed to a public GitHub repository probably four times in the past two years.
In short -- life happens but then the jobs dry up and good talent is over looked or lost.
And, yes, it does happen to women more than men.