It is understandable that you would feel as though this guy wasted your time.
He may have completely ignored you and never said a word because he felt unsure about how to go about interacting with you in real life.
It was a lot easier for him to throw subliminal messages at you on social media because he wasn’t interacting with you face to face.
However, when you showed up at the event, everything suddenly got real.
He may have just felt incredibly anxious about talking to you in a real life setting.
As a result, he may have chosen to ignore you so as not to put himself in an awkward position where he wouldn’t quite know how to keep a conversation with you interesting, continuous and fun.