ACH VERSUS ELECTRONIC CHECK

My company recently made the switch to Quickbooks Merchant Services.  I emailed one of my customers an invoice with the pay online option enabled.  The available options for my customer to pay his bill was buy either credit/debit card or ACH.  Rather than choosing either of those options my customer decided to mail a paper check.  I asked him why he didn't submit the payment online and he stated "his bank charges him a $12.00 fee for ACH wire transfers, but nothing for electronic check".  Since only ACH wire transfer was available and not electronic check he chose to mail in the payment.  My question is, when a customer chooses ACH payment through the online payment in Quickbooks Merchant Service's, is it considered an electronice check or a true ACH Bank Wire Transfer?  All responses will greatly be appreciated.