It might be confusing in the photo, the line exits the rudder head and runs along the bottom of the tiller to a clam cleat. It is not so much of a
downhaul, but more of a hold-down to keep the rudder blade from riding up in your wake when you're up on the step and doing 30kts with a rooster tail! LOL
Some sailors replace the clam cleat with a quick-release to avoid rudder damage in the event it hits something. HTH