Ben, having been SENT the coins, whether mistakenly or not, now owns them. The network was informed of the transfer of ownership by phantomcircuit and then confirmed the transaction by including it's data in the blockchain.

164.065 Theft of lost, mislaid property. A person who comes into control of property of another that the person knows or has good reason to know to have been lost, mislaid or delivered under a mistake as to the nature or amount of the property or the identity of the recipient, commits theft if, with intent to deprive the owner thereof, the person fails to take reasonable measures to restore the property to the owner. [1971 c.743 §126]