I like the subtlety of the one leg rooting: it's the arm that is destabilising the pusher so that they can't use full direct force.
The biggest thing I learn from the video is not to push at the hips. It's like Sunzi says: use the strongest to defeat the weakest. You would have a much better chance pushing the shoulders using your whole body rather than the hips.
A good application of that theory is when he counters the whole line of people. The weakest aspect of the human chain is the connection between the links.