The water is held that way due to surface tension and rotational momentum. I think you'll find you need two people to make it work really well. One person holds the top of the glass down on the table and the other rotates the glass for a while in order to build up momentum. The one which worked, he rotated his hand anti-clockwise, then lifted, whereas the three failed attempts he twisted clockwise - probably not a factor, but might be something in it. Water swirls down the toilet differently in the northern hemisphere.
He uses a plastic tumbler and one with a defined angle and simple shape, not a glass and not a shape with a curve.
The other thing might be some olive oil (or similar) in the glass which reduces friction between the glass and the water and helps the spin. This may be important as the water is rotating (moving) and this suggests the glass needs to be seriously rotated prior to the lift.
Why didn't this come out during school holidays?