That is a classic pickup line, you know? Walk up to a girl and compliment another equally beautiful girl. This usually triggers a bit of jealousy and the guy seems increasingly attractive out of competition with the other girl.

Anyway, as a guy I don't see any reason for you to respond if you are not interested. Your response will result in iPhone push notifications and emails that will trigger positive emotions only to be swept away the moment the message is read. It's really not constructive or beneficial to either party.