It looks like the horse has done this before. Maybe the local horse dealer worked out a deal with the sirens? The horse is trained to lead the fool to the sirens, then to come back home, to be sold to the next fool. The sirens get a steady supply of prey and the dealer gets to sell the horse over and over again.
I kinda like the idea of the man getting taken and the horse being left alone (apparently). At least his muzzle will be less itchy after the gear is removed.