Was it against a bank (ie, debit) account? If so, it's a pre-note test, fairly standard in the industry to ensure a direct-debit or direct-credit can be assumed safe.
This unit tests both the debit (of e.g. $.01) and a credit of the same amount against the target. They can also vary the amount, then ask the recipient to report the amount posted (so you can prevent additional fraud that way - attacker may have your bank account/routing details but no login to your statement/transaction listing).
It was definitely processed through the MC network, and not via Direct Debit (the closest UK equivalent to pulling funds via ACH).
I know this because the vendor didnt have my bank account number, because Direct Debits are processed in batch (not instantly), and because the app associated with the account showed it as a card transaction.
This unit tests both the debit (of e.g. $.01) and a credit of the same amount against the target. They can also vary the amount, then ask the recipient to report the amount posted (so you can prevent additional fraud that way - attacker may have your bank account/routing details but no login to your statement/transaction listing).