What an interesting bit of history! Even though that tree isn't old enough to have been shaped more than a few decades ago, I bet it was done by someone who knew the history of the tradition.
When I was a child, we would look for trees that had trunks that had been bent with a portion horizontal to the ground, making it possible to ride it like a horse. That was fun!
I just learned something reading your post. I had never heard of a "trail tree" before.
What a really great find! Really exciting for you to find one! Locally we occassionally come across old Stills in the woods, its really neat to find one. Thanks for sharing it!