The claim is false as the way the syntax is worded states that the word is not spelled the correct way. If you are to follow up to say that the word is spelled as given in the first example and that every definition is spelled the correct way by spelling "incorrectly" then you would say the following. The word "incorrectly" is spelled: "incorrectly" in every single dictionary.
It's better to test someone by saying "Gullable" is not in the dictionary. When, in fact, it is.