A very competent developer who is interested in doing some ML work may have just recently read this article and gotten to work on an ML project because he feels that not doing so will hurt his chances of getting a job.
As a note, I have no idea what the right solution to this problem is, it is good to confirm candidate's knowledge (I prefer creative ways similar to the parent) and part of that knowledge certainly can include open source work, but going down this road too much leads to people feeling obligated to make open source work to put on their resume and even to people faking open source work to try and land a job.
...which makes the world a better place. Why do you object to people writing open source code?
i do have one concern if it ever became an industry prereq, it becomes a filter for those who have more free time to work on side projects.
I think it is absolutely immoral (and dumb from an IP risk point of view) for companies to try to get interviewees to solve real problems for free.
This is different though: this is about potential candidates finding creative ways to demonstrate their skills.
The companies didn't even ask people to do this: these people chose to take on projects that would demonstrate their skills in a new space in which which they did no yet have commercial experience. I think that's commendable and a very smart strategy.