I don't even think the brain has a way of creating truly random ideas, everything is a composite of something encountered. I think the thing people mean by "creative" is "unfamiliar". It doesn't have to be something that's completely new, it just has to break a norm and do it well. And people have to think it's actually creative, and not just random and stupid. I don't think I believe in originality that much, I know where all my ideas come from, they're inspired by things I enjoy, and would like to replicate in my own image. I think any artist and musician truly knows where they lift their inspirations from, and if they claim it just comes to them in "true inspiration" or some divine message, they're either lying or not self-aware enough to tell from were in reality they lifted the idea.
I think this might be the appeal of indie games, since they aren't so bogged down by external sources when it comes to where their ideas come from. But even in the realm of indie games, many (and arguably most successful ones) are very, very heavily inspired. Just look at Shovel Knight, a castlevania clone. Axiom verge, a metroid clone. Or even Freedom Planet, a sonic clone, which we watched come to existence from a literal sonic engine.
But being able to identify the sources of inspiration don't make them bad games, or devoid of creativity, or their own ideas. So I think the most important thing here is just to make whatever you're doing fun.
(and cite your sources)