Back when I was practicing to hold my breath for a long period of I time I did some research into this, and it really does look like there's no damage so long as you regain airflow within a few seconds.

It goes against common intuition, but it's not like that's unheard of when it comes to the human body. Look at intermittent fasting for example.

It's a reasonable assumption, but that doesn't have much bearing on whether it's accurate.