His actual words: “This'll either fix it or blow it up.”
This video was posted by a man who said he took his car in with a knock that was likely being caused by some carbon buildup in the cylinders. He also said that what the technician then decided to do was run the car around town in first gear, bouncing it off the rev limiter the whole way. It is certainly true that this could clear out the carbon, assuming that was the problem. It could also cause quite a bit of damage to several different parts of the car.
As we understand it, the legal ramifications of this story have not yet been settled, but it's safe to say that someone was doing something they weren't supposed to.