What you are describing sounds more like the author's definition of homeschooling than unschooling. That said, he is teaching them the skills to run a farm, so at what point are you exposing children to something rather than instructing them.
You have to do some instruction around the edges, but largely the idea is that you offer different avenues for exploration and then they choose which way to go. Homeschooling generally has a fixed curriculum, often as restrictive as traditional schools - so that is the distinction.
