It doesn't seem to be a very common drop. Maybe someone wanted it for transmog? There's no accounting for taste, and people do pay too much at times. Just a theory.
Blizz does make mistakes. I got a swept up in that ban wave from the bag exploit. My crime? I did all the pet dailies and waited until I was done to open all my legally acquired bags. Ban was later revoked but I still lost 2 days play time for doing nothing wrong.