I am unable to link to it now. I think I saw it on both platforms, but am not sure. On at least one! If I remember right, the purpose is to entice students to not dread being the first to answer. If the instructor posts anonymously something partly right but obviously wrong in some ways, it might indeed encourage discussions. The morality/ethical worry is exactly the reason I would not use it, or at least not without some evidence that this is a good idea.
I have wished several times in my online classes that someone would really really really speak up/ask a question/etc, but have never resorted to that. It feels like cheating somehow, and potentially damaging to the profession as a whole (pushing agenda, manipulating students, etc).
On top, some students are much much much more digitally literate than others, and this surfaces in the manipulation they do of other students for their own gain.
For instance: in a course where one is rewarded by “length of discussion generated”, one smart student might ask a question relating to something that is obviously irking all students (say “Why can’t we have the slides of the instructor?”). This is bound to generate a discussion, that the profiting student can themselves keep alive by posting further anonymous contrarian posts.
Indeed, if the instructors go down that route, it becomes much harder to “police” students as well and foster good community.