Nassim could argue that its a "greater fool machine", but its literally not a ponzi.
I had always understood a ponzi as being something paid out by later investors, and where you had a plausible reason to believe in increase in value.
Here the plausible reason is “bitcoin will take over the financial system and everyone will need it” or “bitcoin will be the new store of value and everyone will want it”. In either event payout necessarily comes from later investors.
Ponzi appears to be an income-producing asset, but the income is paid out from the principal.