I'm not going to answer your question directly - others have done that already.
I will say that, as an older man, my brain has thrown up random things from my childhood multiple time, so the same may happen for you. I'm no psychologist, and I'm also late-diagnosed autistic, but it seems that the brain can lock away memories from that period because it didn't know how to process them. Then, much later in life, it'll dig one up, dust it off, and put it at the forefront of your mind and say, "Go on then, you're all grown up and know so much now, what about this then?"
This has happened to me at times of trauma (like I didn't have enough to deal with at that time already - and may be the same for you with your OCD), but also at times of peace. I had a traumatic childhood which I won't go into, but it's provided a rich seam of suppressed and painful memories to randomly spit out and obsess over throughout my life.
I think my point in writing this is... Just to say that you're not alone in having random thoughts from your past take over, and that overall I don't think it means much that it's come back to mind.