The arbitrator closed the trade by the seller’s request. He sent the payout back to the seller. However, the XMR payment was already sent and the ‘sent payment’ button was pressed before the dispute.
The arbitrator did not ask if I had sent the payment before closing the trade.
Arbitrator’s address: hvllnddukspprwt6.onion:9999
EDITED: removed the txid and key for privacy