Yup, could have been messing with you. I had a kid do that once. I missed him, but barely, but before I went by I saw the gleam in his eye, and I knew it was on purpose. Your kid was darned lucky it was you and not somebody going 30 mph. On the other hand, you can't always tell by looking at someone that they are "normal". The adults with him had some responsibility too.
I rode yesterday too, and had a completely different experience with kids. There was a family, mom and dad and three kids, all three kids on little bikes, maybe 4,6, and 8 y/o's, with dad bringing up the rear. They were all on the right side as I approaced from behind, but you never know with kids. I rang my bell and the dad told them all to get over someone's coming. I think it was a game for them to see how close to the edge they could get without going off the trail. Would that they all were like that.