Even the shopkeeper is depressed by that answer
ngl i feel like it was her not being serious about it. it's like if you see two people with matching rings on their ring fingers, holding hands, and making googoo eyes at eachother and they tell you they aren't married, just friends. they aren't fooling anyone but rather than call them out on it, you play along to humor them.
notice how she never stops calling him naomi mr boyfriend even after this apology.