Customer thanks salesperson, but not sure why

During a sales transaction at a popular retail outlet, a customer rolled her eyes while listening to the two co-workers gossiping about someone who worked at a strip club while waiting for the sales associate to finish up the transaction. Even though the salesperson didn't provide any special service or barely acknowledged the customer, the customer thanked the sales associate anyway. As the customer left the store, she realized she had no idea why she thanked the sales associate and why the sales associate didn't thank her instead.