To just walk away is going to be (quite reasonably) perceived as rude. I mean 'she wanted you to talk to her' so you somehow got that signal and she saw you ponder it for a moment and then walk away. You could have just said something simple, made your excuses and then moved on. Looks shouls be irrelevant in the way you treat a person. Her annoyance was most like due to that and not so mich being 'rejected'.
I think everybody gets upset at some level, when their feelings aren't reciprocated
I agree. I think that before we act we should put ourselves in the other person's shoes and ultimately not do what we wouldn't like to be done to us.
Ghosting it's a very common attitude nowadays but I think it's a horrible and cowardly way to deal with people. We can and must do much better than that.
We must remember that other people have feelings too and what may be totally insignificant to us may be totally the opposite to the other person.
In addition, we don't know what other people are dealing with at that moment in their lives so we must be careful how we deal with each other. Sometimes it can be the last straw for that person.
Regarding the permise that attractive people have plenty to choose from and don't suffer it's not entirely true. Yes, they usually have plenty of options, but it doesn't mean that they want those options. And of course they suffer and are also rejected.
The world is completely lost. I have already given up that part of my life.