Also rest of the article says he asked students objecting accusations to tell what Marxism is and they admitted afterwards.
Yes, I read it. All of it.
He definitely caught a number of them, but he called it proof, it should NOT be treated as proof, an indicator at best. If it were proof he could just fail them all and not catch false positives.
Totally agree about the number of people to interview being expensive. But it is more adequate as proof.
What he didn't do wasn't wrong, but he can't count on that to be a point to fail.