I have one of those exposed root satsukis, though I didn't make it myself. From what I could see at the nursery, it looks like when he transplanted the tree he squeezed the roots together into a column of sorts and wrapped plastic wrap all the way around them. This would force all the roots to grow down not out. Then, I imagine he gradually exposed the top of the column as more roots grew out the bottom.
I bought a couple extra small ones that had not had that done to them yet, with the plan to try to do it myself. But I had a hard time keeping azaleas alive where I was living at the time. They croaked before I had a chance to work on them.
Now that I am living in a more temperate climate I should try again.