I’ve seen it fail, having tried it for a few years. There’s a type that passes this no problem but isn’t productive.
I switched to a battery of knowledge questions centered on the type of programmer I was looking for, it works much better and is even predictive of coding ability as it helps you learn this stuff.
I'm curious, how can he be so sure? How does he know that he has never failed a competent programmer or that he has never passed a poor programmer?
Just because he hasn't seen it fail, it doesn't mean his process hasn't failed.