This question was voluntarily removed by its author. The author then deleted their account.
Generally, when the author deletes their own question, the "not found" error message shown to <10k users says:
This question was voluntarily removed by its author.
However, if the author deletes their own account sometime after deleting their own post, the notice changes to:
This question was removed from [site name] for reasons of moderation. Please see the help center for possible reasons why a question may be removed.
...which is shown on questions deleted for any reason other than by their author.
I believe this is incorrect; it should continue to show the former error page on voluntarily deleted questions even after the author's account gets deleted.