Syag – “what here qualifies as motzi shem ra?”
Syag, I’m sorry, but I don’t quite understand your question, as you yourself stated that you thought it was problematic that CA brought this up in a public forum.
It is Motzi Shem Ra because he is posting a criticism of the person/people presenting the story. That is Loshon Hara/Motzi Shem Ra and it is assur. According to Halacha, you are not allowed to criticize a shiur.
If you want to know why I used the term Motzi Shem Ra instead of LH, it is because when someone speaks Loshon Hara, it is assur for me to “mekabel” it, and therefore I am required to relate to it as though it is false (and t/f Motzi Shem Ra and not LH).