> No, the money is sanctioned, he has to block it from being used anywhere and he must report it within 10 days according to the law

This is not correct.

> U.S. persons may have received unsolicited and nominal amounts of virtual currency [...] from Tornado Cash

Because he did not receive those funds from Tornado Cash. He received them from a third party. This third party has interacted with a sanctioned entity (Tornado Cash), but sanctions are not transitive.

You can test this easily w/o cryptocurrency: You may not be allowed to transact with Iran, but you can buy stuff from a Germany company which has business with Iran - until OFAC may want to decide to sanction the Germany company.

The "dusting attacks" the OFAC FAQ refers to are transactions that someone sends directly from the TC smart contract to your wallet.