Antifascist simply means “anti fascist” in the same way “make america great again” simply means “make America great again”.
Sometimes the name a Group picks for itself doesn’t match it’s actual behaviour. Love, the democratic peoples Republic of Korea.
Anti Anti-fascists may not be fascist, however they oppose the people who oppose and fight against fascism for one reason or another.
Everyone who is a part of antifa believes they are actually fighting fascist. And thus they call them selves Antifa, if they believed otherwise they wouldn’t call them selves Antifa. This is literally true by definition. A pleonasm if you will.