> Revlon's bank repaid Revlon's loan using money Revlon didn't have. Oops! But that's not clearly a reason for the lender to return the repaid loan.

I think the point about it being money Revlon didn't have is important. The money came from the bank's accounts, not Revlon's. The owner of that account (Citigroup) had no debt owed to Brigade, so I don't think the bill pay analogy is quite apt. This seems like nothing more than an accidental transfer, which happens all the time and are always reversed.