Most trans flush services are not a "backflush" design. There's two main types of machine, one is a pure transfusion machine, it goes inline(series) with one of the cooler hoses, the transmissions natural operating pressure pushes it's old fluid out into the machines empty bladders, this then displaces the same amount of fresh fluid into the trans on the outlet side.
The second machine operates through the fill hole or dipstick with two hoses. A fill hose and a drain hose. The fill hose is shorter and doesn't reach into the dirty fluid. The drain hose sucks dirtty fluid out of trans then the fill hose injects a quantity of new, the machine idles for a bit, and repeats this process multiple times.
Neither of these flush types force the debris in the fluid to circulate anymore than normal trans operation does.
He is saying that he does just a modified more complete version of what most guys here do. That being a drain and fill. Difference is he allows it to run with the trans OUT cooler line disconnected to have the trans force the old fluid out without recirculating it into the new fluid. (Much like the transfusion machines do). His way is not new or novel, it's better than drain and fills, but is definitely more labor intensive, and provides much higher degree of making a huge mess LOL.
This actually the current GM procedure for flushing the 8 speed RWD models with problematic fluid fills