You don't exist

He woke up bit early that day. It was a delightedly refreshing morning, he felt. He got ready and went to his regular beach for jogging. As it was early there were hardly anyone on the beach. He kept jogging by the shore till he stopped to catch a breath. As he was admiring the long  straight tracks left by him, someone tapped on his shoulder. He looked back to see who it was to find that it was a woman he didn't know. She just said, "You don't exist" irritated, as he was about to respond, just then the woman gestured towards the track, he had been looking at. As he turned his head, he saw a wave wash away the track. Not being able to correlate, confused, he turned his head towards the woman to find that she is already on her way. He stood there for while with grim look on his face. After a while he started walking towards his home.