Bishop lets us know right from the start that Man-Moth isn't her word.
She's also kind enough not to reveal who might be to blame for what was probably a pretty embarrassing mistake. She did reveal in an interview almost thirty years later that the misprint was in The New Yorker.
Since the word came from an error, we get a really good idea that the Man-Moth is a fictional character. Knowing this from the beginning tells us to go ahead and put on our fantasy glasses and prepare for a suspension of disbelief.