Bitcoin's new record price means that Satoshi Nakamoto is worth $5.9B

Or borrow against it.

Or that he even has the private keys. Or that the markets don’t freak out the second he moves a penny.

*presuming that Satoshi is not Hal Finney, who is dead.

^ this. He's probably banking that BTC will at some point become the de facto standard for currency, and he will be able to simply spend his BTC.