The continuous hand gesture is sampled and digitized by the software. It causes a loss of the original body gesture but it captures the accumulation of time only affordable by the technology. It's not only the lines but also the process of drawing that is visualized.
The software that is used to record the movement plays it back. It's like the Cinématographe Lumière was both a camera and a projector, but the software can do both at the same time.