Sometimes important encounters occur in the blink of an eye. Literally: the eye flashes aside for a moment, alerted by a subliminal image, and into that eye falls that other person. In this case, a horse caught in sheep wire.
It could also be that the horse was calling the man telepathically. Horses can do that, especially if they interact with people a lot, and this is an old greengrocer's cart horse.
The man frees the horse and goes to take...