First off that video was a crappy example of the reverse sear concept...I will explain...
The Theory...When meat is seared/grilled over high direct heat, as is typical in most backyards, a lot of energy is pumped into the meat over a short period of time. This causes the meat to be very well done on the surface, medium through most of the meat with a rare or med/rare thin strip of meat in the center only. Additionally when tested there seems to be more moisture forced out using this method.
In Reverse Sear the same meat is cooked gently over low heat until Rare then we put the spurs to it over high heat just to get that crust and flavor. The result is a more uniform doneness across the bulk of the steak and tests show it seems to stay moister.
My take...This only works on Steak 1 1/4" or thicker. For the typical 3/4" grocery store cut steaks, reverse sear will guarantee well done meat! If you apply a little skill and timing you can do what a lot of Chef's do in restaurants. We give the meat a quick sear then go over to low heat to finish. This is what the guy in the video did, Hot Sear then finish low and slow...That is why he could not see a difference. They ARE essentially the same doing it this way, that is why the video is a poor example.
Where reverse sear has a Huge impact is if you wish to add Smoke to the steak...Giving the meat an hour and a half of cool smoke 150* will get some good smoke on the meat and still keep the meat very rare on the inside. Then you Sear it to get your crusty goodness and achieve the final IT you wish. I hope this clears thing up...JJ