To Shreedhar's point, it's more accurate to say the concrete, valid, non-mythical existence of the Hallows wasn't well known. That being said, it's obvious that's what you (Alex) meant, it's obvious within the context of your answer that's what you meant, to the point where @Shreedhar is essentially committing an equivocation fallacy, where he's switched out your in-context definition for Hallows (non-mythical) for another definition (they are mythical and legendary).