The atg.commerce.csr.returns.ReturnTools.createRefundMethodInstance(String) method creates a RefundMethod instance based on the refundMethodTypeClassMap property value. If the given type is configured with a RefundMethod class, a RefundMethod instance is created. The payment group class type is used to create RefundMethod instances.

The default configuration for refundMethodTypeClassMap property is:

/atg/commerce/custsvc/returns/ReturnTools.properties
refundMethodTypeClassMap=\
           creditCard=atg.commerce.csr.returns.CreditCardRefundMethod,\
           storeCredit=atg.commerce.csr.returns.StoreCreditRefundMethod

When ReturnTools creates a RefundMethod, it will use the type value and create an object of the class you identify.