Kurt, the list you link to are actual corporate Apple Retail Stores. The Klarna Storefront is a virtual store that you link to through the Klarna website. Many corporations have online stores for employees or in the case of banks for their cardholders to access and redeem points etc. For example Chase Bank has one for their cardholders to redeem points.
The Klarna card is added to Apple Wallet and used at checkout by selecting Apple Pay. At an Apple Retail Store the customer uses Apple Pay and pays with Klarna card presented in Apple Wallet. Customer then chooses a payment plan and Klarna approves or declines the transaction, like any other Apple Pay transaction.