I posted the other day about my Proofs quiz that nobody seemed to complete. Last night we got the quizzes back. I got 10/10 on it, but unfortunately my professor doesn't discuss the overall grades with us, so I don't know how other people did. (The woman next to me got 6/10.)
But there were hints. The professor told us he would drop our lowest hundred consecutive points. He also told a long story about taking his grad school prelims and totally blanking out and feeling like he knew nothing and could not even get started on the things he had to do. So he said he understands how you can blank out or have a bad day.
I conclude from this that my surmise was correct.
He did also go over the proofs that were on the quiz, in detail, and at least one of them could have been done in a much shorter way than how I did it. His grading is kind of capricious, and it's hard to guess how much explicitness he wants in the proofs, so I tend to err on the verbose side.