You can't tell if the cars loosing any kind of grip due to what every the conditions are like as all you see is a speedo. The point is its not changing up a gear, if it did he would aid traction by lowering the revs.
Yes, if he changed up a gear it would create more traction at the wheels but if the car has not gained any real momentum yet, then would just bog down as there would be no speed.
Wheels speed=60mph, actual speed=10mph, change up to 2nd or 3rd and it would be the same as trying to pull away from a standstill in 2nd or 3rd gear.
You don't need to see the road to hear what's happening although it would be nice to see.
To me, it's Go, wheelspin, wheelspin, wheelspin, wheels slowly gaining traction, wheelspin, wheelspin, wheelspin, car speed increases, wheelspin, wheelspin, car eventually matches the speed that the speedo is showing which is already on the limiter, then change up as wheels have enough grip to get the power down
As for if you can change gear manually or not with the DSG, I have no idea, but I do know that whoever was driving in the vid either wanted to thrash the poo out of the car or simply don't know
how to get a car off the line quickly! lol