At worst, it’s gauche. It’s much more likely that the moderator was personally offended by the use of that word than anything else. I have my own pet peeves. I can’t stand the sound of someone saying “an historic event” … but I’m not going to go around banning people over it. All that’s going to do is make everyone more and more angry.
This is why we put specific, actionable rules on communities, people!
Oh, I’m not actually angry about it. That said, I ask you: if an hat, an horn, an hobby, and even an hydrogen atom can all be preceded by “a,” why should “an” be attached to “historic” as if it’s an hero in an heaven of English grammar? Bring back the aspirate H!