This is a little weird even for me, but intriguing as hell.
It's normal for a tiny number of cells from the draining parts of the urinary system to wash away in urine. Throwing off very many is not healthy. However, given a tiny number of healthy cells, they managed to tweak the epithelial cells (the cells that form the "skin" of a space) of the renal system into being able to turn into a variety of other cells, including nerve cells that could grow and connect to other nerve cells.
Caveat emptor: manufactured stem cells are not like Mother made. There is always something they do that's not in the original specification.
This article makes the point, at the end, that this is a starting point and that the stem cells it produces, and the differentiated (that is, specialized) cells that grow from them, really need to be evaluated before those of us who need new nerves (or kidneys, or whatevers) should start to cheer and break out the champagne.