Another principle at work here is "tun, tu" (or swallow and spit out), when he does it with one hand the swallow is very small and the yin ru yang chu principle is 3 tight small circles. Later he shows it more obviously with 2 hands.
At a recent I Liq Chuan seminar, Sam Chin also demonstrated tun tu
in different ways as part of what he calls "absorb and project." I'll see if I can find a video clip where he demonstrates this overtly.