That is just the ignorance of people without a classical or literary education.
Only because the majority doesn't know anything about the concepts of connotation and technical terminology, it doesn't mean that both doesn't exist. For example, the simple word "action" can mean something completely different depending on whether you are talking with a normal person or a lawyer. The same is true for incompetence, ignorance, etc. etc.
So, if you are talking about fiction in literary terms, then fiction has little to do with being "fictious".
"Most English originated from greek roots" An interesting claim, do you even know Greek? Or rather, can you even distinguish between Greek and Latin?