Footnotes to Aristophanes

On Radio 4 Edith Hall has just been talking as if everything the character Aristophanes says in The Symposium was said by the real Aristophanes - with no hint of a caveat. I'm no classics professor (obvs) but I assumed Plato made it up? (Aristophanes wasn't around to sue by then, after all.) Does this mean that in future years we must expect every word spoken by a "real" person in novels and biopics to be treated as genuine by future Ediths Hall?

This seems such a basic and obvious error that I wonder whether I'm missing something.