First, set your camera to 61-point auto focus mode, then select, if you'd like, the center focus point.
Next, press the button that looks like a + inside a box. While holding this button, press the light bulb-looking button on the top of the camera. You should hear a beep, meaning that you've registered 61-point auto focus mode, with the center point as the registered point.
Now, press the Q button, then select the button that looks like the camera shape, with the text-like lines to the right of the camera. This will take you into the Custom Controls menu.
Select the DOF preview button option, then select the "Switch to registered AF point" option, which will assign the DOF preview button to 61-point auto focus mode. Note, if after setting you go back to this option and press INFO, it'll bring you to a sub-option, which you can use to make sure this mode is only active, while the DOF button is pressed.
Finally, reset the auto focus mode to whatever you normally use, for example, the + looking option (single point, with 4 assisting points surrounding it.)
So now, you should have your camera in + autofocus normally, but hold the DOF button, and you'll be in 61-point auto focus mode. Sorry I didn't use the correct terms for everything, but I just didn't want to look it all up. LOL
Hope this helps!!!
BTW, if your camera is in servo mode, it will try to focus upon the specific focus point you selected, for example, the center point, then track it as it moves about the 61-poionts. If you're in single shot AF mode, it will focus upon the closest points to the camera, which is how it was shown in the video. Have fun!!! I just love my 5D Mark III!!!!!