It was a smallish dog, about 10 lbs. He had his back legs strapped to this aluminium contraption that had wheels on the front. So the dog was more of less horizontal and his front legs were doing the walking while the contraption wheeled along behind him. The dog did not appear to be unhappy at all and he did not appear to be injured in any way.
Did he have back legs? If he had legs, they are probably either paralyzed or immobilized (injury. surgery etc) and this allows him to still be mobile. If he didn’t have rear legs, then, again, this allows him to be mobile.
Dogs susceptible to degenerative myelopathy and others with proportionally long spines, like corgis and dachshunds, often suffer injuries that result in them requring wheelchairs. There are several manufacturers that specialize in them and breed groups that help people borrow or buy them. There’s a Facebook support group for corgis who use wheelchairs, but others are welcome. http://www.facebook.com/group.php?gid=57598352536