This quote does not appear to be from the actual story, so I am assuming that it has been found in some publication that tells you information about the story. In a sense, the quotation does explain the reactions of the anonymous man as he returns to this patch of English countryside where he grew up, although it appears to be so foreign, and the conflict that he has with the horse who dominates the short story. Note for example how the man reacts once he has reached safety:
The ordeal with the horse had already sunk from reality. It hung under the surface of his mind, an obscure confusion of fright and shake, as after a narrowly escaped street accident. There was a solid pain in his chest, like a spike of bone stabbing, that made him wonder if he had strained his heart on that last stupid burdened run.
It is left extremely ambiguous as to whether the incident with the horse actually happened or not. It is highly unlikely that any real horse would pursue a man in such an intent and malevolent fashion, and it remains uncertain as to whether the horse represents the man's own past or another troubled aspect of his psyche. After all, the man has come to visit his past, and perhaps he finds exactly that, but in a way that extremely surprises him.