What does Farquhar believe has happened to save him from a death by hanging in "An Occurrence at Owl Creek Bridge?

Farquhar believes that,
when the sergeant stepped off the plank on which Farquhar was balanced, he "fell straight
downward through the bridge [....]; he knew that the rope had broken and he had fallen into the
stream." He thinks that his noose broke rather than hold his weight and that he has fallen
into the Owl Creek below. He pulls the rope away from his skin and swims toward the water's
surface. "His neck ached horribly; his brain was on fire, his heart, which had been
fluttering faintly, gave a great leap, trying to force itself out at his mouth." He feels
bullets begin to strike the water around him, spraying his face, and he tries to swim as fast as
he can away from the soldiers on the bridge. Essentially, Farquhar feels as though he is
incredibly lucky that the noose broke, he fell to the water below, and now he has the chance to
swim away with his life.