That's such an interesting question to ponder :). I've always had a vivid imagination - so much so that teachers always complained to my parents about it. I think the term "vivid imagination" in code means "she bores easily and doesn't want to listen to the teacher drone on and on"....
I daydream all the time, to the point that at times it does leach into my real world daily life and become problematic. I find the worlds in my head are far more interesting than my daily mundane tasks to be quite honest. I wish I fancied myself a fiction writer. Ironically, I am lost in my imagination all the time, but I struggle to write fiction and do best writing very "real world" stuff. I write marketing materials, product descriptions and directions/how to's for my clients. Even my hubs are "real world" centered lol.
It's perplexing. I would think to write fiction though you would have to be a daydreamer and as such have at least the ability to disconnect from reality for long enough periods to indulge the fantasies to get them on paper.
I would not find it surprising at all that great fiction writers would be people considered to be a bit "out there" in their approach to "reality"... Who's to say what is really real anyway? :) For all we know we may be the characters in some great fiction somewhere lol