Having worked on control systems a long time ago, that's a 'nothing' statement: the whole job of the control system is to keep the robot stable/ambulating, regardless of whatever disturbances occur. It's meant to reject the forces induced due to waving exactly as much as bumping into something unexpected.

It's easier to stabilise from an operator initiated wave, really; it knows it's happening before it does the wave, and would have a model of the forces it'll induce.