He picks a good activity; yoga. It specifically works on balance. That's what's needed for walking and sitting unsupported. There are other programs (like dancing, gymnastics, etc.) that work on this. He does something that all of us do- he gets back up when he falls.
The getting back up and doing it over strengthens the neural pathway. There is science in persistence! If you want to get better, do it over and over. It may be bad the first time you do it, but it gets better as you do it over and over. There may actually be growth of your neural pathway which you can't see. You may think you just did it over for nothing, but really you were making your neural wiring grow.
Some info on this man. "Meet Arthur Boorman, the star of the latest video to wow the Internet. A former paratrooper who served in the Gulf War, too many years spent jumping out of a plane left him with chronic knee and back pain—issues so severe that doctors told him he’d never walk unassisted again. And for more than a decade, Boorman believed them. But then one day he bought some videos from DDP Yoga—that’s yoga à la Diamond Dallas Page, a champion wrestler-turned-yogi—and everything changed."