Jack's New Trick?

So I'm guessing he just got lucky, but yesterday morning I lied Jack on our bed so that I could go get him a blanket. Then, when I turned back around he was completely on his side and continuing to roll over onto his stomach. I know what your thinking, and no, I did not lie him down on his side. He was completely 100% on his back! I have no idea how this happened but I'm guessing it was just a fluke...but it was weird to watch.