All I can think of is that it directs the radiant heat down and out the exhaust system rather than allowing it to remain in the engine compartment. Thinking as I type... if the turbo is water cooled (is it? I think I've heard there is some cooling around it somewhere), if you can somehow manage the heat to direct it away rather than just allow that downpipe to radiate all that heat, theoretically it might help keep the turbo a bit cooler; but I think it's a stretch.
I can't imagine it would do what this guy is claiming... I think this falls in the snake oil category, along with those air intake things that are supposed to cause your air to spin therefore improve mileage, increase horsepower, add zip to your little 4 cylinder car, bring harmony to the universe, make the lion and lamb lay down together, and provide a chicken in every pot and a check in every wallet.