either they sell or shutdown operations, unless they have some other outside money coming in

Miners often operate with high leverage to finance the upfront investment they need for the equipment and such. So when bitcoin pukes to new lows they tend to be liquidated if they can't provide more collateral. That's when the "miners selling" happens. I believe that some did sell the first time btc fell bellow 20k, a few months back.

At least the sats from my home miners are not for sale :)

Zack mentions in the article how some miners are always selling, which is a great point that is usually left out. There will never be a situation of no miner selling, only gauging how much there actually is.