In many cases, other than a letter grade, policy prohibits professors from commenting about students *at all*. Laws such as the Buckley Amendment prevent them from discussing student performance in any way that might be discovered by anyone other than the student, including their parents.
Neither the student nor the class were identified. How could the student's privacy be violated, unless the student voluntarily identified himself?
Many institutions even prohibit professors from issuing requested letters of recommendation,
I have never heard of such a thing, and I've taught college for nine years. Among other things, this would make it impossible for students to get into graduate school.
This also is rubbish.