Notice how they were trained to manipulate the selector with their left hand while maintaining grip with the right hand and magazines stored cartridge down in the mag pouch. I've always done it this way but have never seen it shown or mentioned before.

I manipulate the selector with my right thumb while maintaining my grip, but I also use a SAW grip and extended selector.  With the standard plastic grip and selector, it's a bit more difficult.

I do store my magazines similarly.  Upside down, with the front of the magazines oriented clockwise.  When I grab a magazine, it is automatically oriented correctly for insertion with my left hand.  I usually use my right index finger to press the magazine catch rather then my left thumb like in the video.  I also do what the guy does late in the video with his magazines.  Moves the empty ones to his right side and loaded ones on the right to the left side, and consolidates ammo left in partially-loaded magazines, which are stored between the empty and fully loaded ones.

I'm sure that's not how things really went down.

In the video, they take their sweet time rolling around, changing out mags and putting the empty mag's away neatly.  By the time they're ready to fire again, they could be overrun!

Edit:  I use my right thumb to work the selector lever.  It's right there.