This wierd hoppy feet-lift is something I've noticed over the years on Taiji-related videos, it's a movement not normally necessary for regaining balance after being shoved backwards ... I just concluded it was a learned response which is encouraged by their authority figures and peers. Is that the whole story?
Well, almost invariably you'll see that sort of thing in Taiji that comes from southern China or Hong Kong (the raise both feet hop-back thing). The original admonition about "hop like a bird" got misinterpretted and became something unique to some of the southern styles. If someone gets a hit/push/etc to you, you should not absorb the force (just in case the person hitting is able to generate a lot of force/fajin), and that's what they mean by "not absorbing the opponent's qi". So what happens is that in these southern-Chinese related styles, instead of manipulating an opponent's incoming force when it's do-able or stepping back quickly when it's too much force, they learn to hop to just about every small touch, particularly when done by a 'teacher'.
When I see someone doing that hop I know pretty surely that they have somehow probably been exposed to some southern-Chinese Taiji and that everyone in the class does that hokey hop.... it's almost a hallmark of S.C. Taiji. Someone with competition judo, wrestling, MMA, etc., is going to just laugh and throw them in a more serious confrontation.
Incidentally, Aikido and similar Japanese martial-arts also have a hallmark move when there are no jin/kokyu skills being taught in a class: they shift the hips to an incoming force instead of using the mind (what Ueshiba called "the Divine Intent") to adjust the kokyu/jin path.