I agree that YC's requirements are more flexible than most jobs.
If you don't have the skills to do statistical modeling, we wouldn't hire you. We gave guidance in the job posting about who was a good candidate. But we didn't prevent anyone from applying.
YC is the same in all those dimensions. If you don't have the skills necessary to build a successful startup, they won't accept you. YC gives guidance on their web page about who was a good candidate. But they don't prevent anyone from applying.
I'm not sure how you define "open" so that one of those qualifies and the other does not. If "open" just means that they have more flexible requirements, that is a difference of degree, not kind.
YC is an unusual combination of selective and eclectic. But claims about "the most selective open application in the world" suggests a lack of perspective.
Rhodes and Marshall have specific requirements, even your job hire probably had requirements (high-school education, must be able to lift 30 lbs).
That's what makes YC so amazing... anyone, anywhere, can apply.