The thing about the original post though, the girl knows the guy in person, and she ignored him after accepting to meet - that's bit rude.
If I were you, I would ghost her too....partly, and if you meet her again in college don't walk to her way to say hi, she won't do it. If she passes by within 45 degrees within sight scope and she doesn't react, then do the same - she probably won't.
Unless if you bump into each other by chance, face to face, then you can say hi or nod slightly just out of courtesy and for not showing any grudge, but go on with your route while you are saying Hi, don't attempt top stop to start a conversation.
Ok, here a short real story, there was a girl I met like back in Feb or March, and I had a good interaction with her frequently and she was giving me details of her life like where she lives and where she works - I realize now that I was obviously showing interest in her because the moment I saw her every time I attempted to talk to her.
She turned out we have mutual colleagues - so I told her I ll add her o fb, later on at home I sent her a message and friend request, we chatted several times, it was about sports and activities, nothing about dating or things like that; then I told her I sent her a friend request - she ignored that message completely, she ignored another Hi there next day, both were read (facebook shows you if message was read or not).
So....I've applied the ghosting policy above ever since, at first few times I kinda forced myself not to go after her when I saw her but later on it became natural as If she became a total non-significant acquaintance to me.
There was once instance of conversation during all this period (after my ghosting policy), and it was by complete chance.
On September 4 (just checked my fb chat now
), she accepted my friend request and chatted with me, after about half year, what gives? But my interest in her is totally dead. 