Ok... thing is it's all connected.
It really all starts in the cerebral cortex with the intent to move, travels down the neurons (is it the pyramidal tracts?) to the biggest muscles first, and travels outwards to the smaller muscles. Any more detail than that and I'm out of my depth. core musculature acts to transmit the work done by the big muscles in the lower body to the limbs. Essentially, it's all connected...
However - the fellow moving the boat in the movie is doing real cormorant boat rowing, with a real boat. I wonder what would happen if we actually learned how to do the movement with a boat, rather than some imaginary (or real) person holding our wrists, and then moving to people. that's if you want realistic training...
There's a big difference in having the core initiate as opposes to the legs initiating. Otherwise, a squat could be touted as being "IS" because it's a "whole body" exercise. There's a no so subtle difference.
Rowing and squatting can be modded to be done in an IS fashion, but you have to know "how"