That's true and technically anyone that doesn't have bitcoin (or a bitcoin owning entity) in their portfolio has a short position open.
So far, that 12 year short position has been a disaster for all of the people (literally every single person) on the planet.
Some things are simply tradeable, and his advice is not “throw money at the owners of a fraudulent casino to say you are short”
Nassim Taleb himself wrote a paper arguing Bitcoin’s value is zero and sold all his Bitcoin. I do not believe he believes it is his moral duty to open a Binance account and make a short on a Tether Exchange