I think this may be badly worded because I had trouble understanding the scam myself. It seemed to me as though the Bitcoin seller got a MacBook, the Bitcoin buyer got Bitcoin, and the MacBook seller got Fiat, which I see as no different from a third-party proxy shopper service.
I also see several comments below saying that they had trouble understanding it as well.
The only thing I could see as a possibility here is that the Bitcoin seller on Robosats, aka the scammer, makes a dispute saying that they never got the fiat because the buyer sent it to the MacBook seller and not them, which is the point of the scam.
If arbitration is used on Robosats and the Bitcoin seller has to lock up their Bitcoin in the trade process, and the arbitration sees that the seller told the buyer to use a different account, then it seems obvious what's going on and the dispute would resolve in favor of btc buyer. scammer loses their Bitcoin Bitcoin buyer gets the Bitcoin, scammer gets a macbook, macbook seller gets fiat for macbook.