That "normal" completely regular sine wave for breathing

I was watching this youtube video https://www.youtube.com/watch?v=-gie2dhqP2c made by ResMed, and I'm rather bemused by their graph of "normal" vs "flow limited" breathing.

Really? A perfectly rounded, perfectly symmetric, perfect sine wave is what "normal" breathing looks like?
Ok, here's what MY breathing looks like when there's nothing interesting going on:

Zero flow limitations, no leaks, nice and reasonably regular, but no perfect sine wave, not even close!

So is this like the square fish in the commercial? https://www.youtube.com/watch?v=aUK0am9qD_A

(That ain't natural!)

You are correct that the breathing waveform is not a perfect sine wave. But the video is trying to simplify the waveform to
Make its point simple and clear for audience which presumably is just getting introduced to sleep disordered breathing.

It's similar to how science and engineering is different. For example according to Pascal's law, pressure in the hose, the mask and the airway should be same as the set pressure. But in reality it's different at all places to a degree and also different for different mask types and brands.