Their main difference is the recording of a Refund.
According to SuiteAnswers ID 9198, a cash sale refund is a transaction that gives money back to a customer who immediately paid for goods or services using cash, a check or a credit card. In other words, this does not impact the Accounts Receivable as this refunds a Cash Sale transaction.
Issue Customer Refund page creates a record of payments you make to a Customer. A Customer Refund impacts the Accounts Receivable as it requires you to select one.
You may check the following SuiteAnswers:
Answer ID 9198 Refunding a Cash Sale
Answer ID 44732 Customer Refunds