Not all autistics lacked imaginative play as children. Generally, play is affected; but it isn't always completely absent. Nor, in fact, even usually completely absent.
For example, I had "varied, spontaneous make-believe play" as a child. But I had a different style from other children. I would play the same games over and over, and while I switched from one to the other eventually, I would persist for hours while other children got bored after twenty minutes; and I'd keep the same game for months while for other children it was only a few days. I also had less make-believe play overall than most children; I spent more time arranging things into patterns, creating interesting sensations (swinging, spinning, looking at interesting objects, etc.), and after about three years old, reading. As an adult, I still spend a lot of my free time organizing things; only now, it's information I organize. When I get interested in a new subject, you're likely to find databases full of facts on my computer, essays written, and an encyclopedia's worth of ideas in my head.
So even if you don't match that criterion, it's likely enough that you probably played differently as a child. Play is how children learn; and autistics learn differently. For my particular cognitive configuration, it made more sense to practice patterns and sensory regulation than it did to expand creativity (though I do have a normal level of creativity, based mostly on my large-scale networks of facts... again, just slightly off the norm).