And some people say they aren't animals. Doesn't mean that it's true.That some atheists would abscond with it is obvious. Nevertheless, to the ignostic they are different things.
An ignostic says that the term "god" is undefined, which means that phrases like "God exists" are meaningless and therefore cannot be evaluated for their truthfulness.
Defining a statement is a requirement for evaluating it. You can't assent to the truth of something until after that something is defined. Since anyone who does not assent to the truth of the statement "at least one god exists" is an atheist, the ignostic, because he does not assent to the statement (on the grounds that he considers it meaningless), is an atheist.