Teken's duty was to ensure a secure transaction, sending the money to one of the users addresses makes sense, nonetheless, it could have been a different wallet and the address could have been lost, meaning Teken's duty was to complete the refund to the address he was provided lastly, not to the one he deemed right. With this I mean, every transaction I've MM'd so far, I've confirmed 10 times before sending the money to a specific address. I know for a fact some people use disposable addresses for some transactions, and even some of them might make one user send the money to triangulate a transaction (meaning Teken would be sending the money to a third party involved in another trade). It was not Teken's choice which address to send it to, whether he sent it to one the user provided before or not. His job was to secure the transaction and therefore he had to make sure both parties ended up with the money/goods safely. The user that received the money on another address provided a new one, and it wasn't taken into consideration. If I, as a middleman, don't check the transaction thoroughly and make sure I'm doing things right, I am to blame for anything that happens mid-transaction, whether it's a refund to an incorrect address (the user in question is entitled to change his address whenever he wants to, as addresses are changed by almost everybody to ensure their privacy remains private).
If this situation were to be applied to real life, if I had given an address to ship a product and then changed it before it was shipped to a new one, and the product was still sent to the previous address without considering the change I made, it would not be my bad, it would be the companies for not being thorough and not doing their job correctly.