comment vs complaint

yesterday I went to have dinner with friends. my food was not so tasty, so I gave my sincere comment to the owner while we're paying the dish. to my shocked, her face turned to 'very unhappy'. even at that point of time she was to receive the money. couldn't she differentiate the 'humiliating' comment and sincere comment? nothing in my comment could be misunderstood as 'complaint'. what happened to maxim 'customer is always right'?