Zhang, Shifu demos in this way to allow others to feel it. Often talked about on the web, known by other names “kong jin” or what some call “empty force”
The subject of many heated discussions on the web, even by those there watching, or in the demos feeling it first hand.
Many of Master Zhangs students have come from other CMA backgrounds staying after feeling something different.
In trying to understand this difference through the lens of their experience, they often find it cannot answer what they see and feel, only something that many years of dedicated practice can answer.
I will add some other clips here from different teachers, with my own commentary hopefully helping to explain what is viewed. This has been a part of my own research, studying , training with Master Zhang and the taiji family there.