Mike Hsu posted this video as an example of something he admired, so let's take a look at what is happening:
The main point I want to make is that nothing is going on here that is not a portion of the 2 major blogs on Reeling Silk and on Jin, although this video relates almost entirely to the Jin blog.
Essentially, the students push in on a high section of the instructor's body and he responds with a force coming from the ground that goes up under and into the students' forces coming into him. There's nothing to speak of in terms of the reeling-silk usage of the body and it goes to show that "muscle jin" can certainly have utility, particularly when used against students who have no idea of how to use basic jin (and are somewhat cooperative). Let's hope that the teacher, Seronko, is also showing his students how to do this fairly simple use of basic jin so they can enjoy doing these things, too.