Honestly, that video is too unscientific to be meaningful. It’s so difficult to draw a straight line on an iPad (since the screen is so slippery), especially with your hand in the air like that, that I don’t think it’s a meaningful demonstration. One cup of coffee could be the difference between the different colors of lines. A much more valid demonstration would use a ruler.
Also, I’d want to make sure there aren’t any potential non-human sources of interference, like electromagnetic interference. While I can’t find anything definitive with a quick search, at least some sources say the position sensing is capacitive. And if that’s the case, then I know for a fact that power supply quality matters. Noisier supplies cause less precise, less sensitive finger touch response, so it would not surprise me in the slightest if it did the same thing to the Pencil, if it is in fact capacitive. If there are other sources of interference, it could have an effect. (I am in no way saying this is likely, just that it’s theoretically possible.)