I think you had good intentions but the flowers probably made her feel uncomfortable. As a woman, receiving flowers from a guy who knows I don't reciprocate his feelings would not make me happy. It puts the woman in a bad spot. If she says thank-you to be polite, it can be misinterpreted as encouragement. And if she reminds him that she's not interested, she's a bitch. Either way it's unwanted pressure because a man giving flowers to a woman is always going to be interpreted as a romantic gesture, which she clearly doesn't want.