That's very interesting. For me, that might be a bit philosophical and not really applicable in reality, but I don't think free will exists, from some point of view nor does pure creativity. Everything comes from something prior to it. Things don't get born in our minds from a blank page. But what we think comes from our creativity is just what comes from a process that escapes our consciousness or is too blurry for analysis. That's like the difference between analysis and intuition. Intuition is just analysis minus the metacognition (the awareness of the analysis process itself) so we just get the result seemingly out of nothing. But I think consciousness/awareness is rather the rule than the exception (edit: no I mean the opposite). When we look closely, most of what happens in out minds escapes our consciousness. When I try to remember something as simple as how many eggs they usually put in an egg box, I know the result but I don't know what process I use to search for the answer in my knowledge about the world. Do I first day "egg" in my mind and then let some images pop up? What elemental steps. And these elemental steps, what are they made of? When my ears hear a word in my mother tongue, in what language is it translated to for the rest of my brain to "understand" it. What is the "meaning" of something? What is a meaning made of in our minds? Everything is obscure. There is so much unknown but we generally ignore it, or put it aside in a simple concept like the subconscious or creativity.
But I think the people who said psychosis had something to do with creativity (probably psychoanalysts) just could not understand what people with psychosis were talking about and so they put it behind this concept with the rest we don't understand, without knowing that everything works in this way. 99.99% of our thought processes are obscure and if they really believe it is not, I think they didn't look closely enough.