"He can't have autism, he has an imagination. Kids with autism don't play creatively." We got this quite a bit when we were thinking about whether Flynn could potentially have autism.
For a lot of reasons, this is silly. One of the stereotypical autistic "traits" is increased associational ability, though your mileage will vary, of course. Imagination oftentimes appears as simple as association of one event with another, so a car is like a Gup (a boat on the Octonauts - keep up, people), and if we are going really fast down the road, it's like zooming through the water, and suddenly I hear from the back seat that "We're in the Gup X, and we're zooming down deep, deep into the midnight zone!!!" Wow, he's so creative!
Scripting can be creative as well. If Flynn says something from a show in a new context, oftentimes he is seeing an association I've missed, as when he spots an emotional or situational similarity between that situation and his current reality. But sometimes he's using a script to express something unique, for example creative use of a funny script to get a laugh in a serious situation.
Flynn also likes to create unique characters, similar to familiar ones. So he makes up sea creatures that are, for example, based on ones he sees in the Octonauts, but bigger and scary instead of funny.
Creation of entirely new situations or characters I haven't seen much of, but I have trouble doing that, and I'm not . . . a four year old.