Even if he knew with certainty that BTC would go to zero in, say, 10 years, that doesn't imply that shorting it would be wise - he could easily have his position blown up due to "greater fools" buying in at even higher prices before it tanks. "The market can stay irrational longer than you can stay solvent" and "being early is the same as being wrong" are both well-known maxims in finance for a reason.