I think you did fine. As a guy with nieces, my standard for how I’d approach a woman socially is how I’d like another man to approach one of my nieces socially. In a public place where she has several outs if she gets a bad vibe from the situation. But also confident and direct. But just because he shot his shot respectfully doesn’t mean you owe him conversation. Being at a mall to shop or to walk or to kill time is perfectly fine. A lot of younger people do use it as a meeting place because it is big and public and you can explore similar interests while shopping, or even window shopping. When I was younger, I avoided the mall because “mall people” weren’t my kind of people, but now I can see the advantage.

I’d ask you how you’d prefer to be approached, but it’s beside the point since you weren’t looking to be approached in the first place, and that’s fine too.