The main claim to fame of the highwayman's hitch is that it can be quickly untied by pulling the short end. The knot just slips out of the ring. Its an easy way to cast off without having to untie a knot by hand. It is not intended to be a very solid knot but really a convenient way to tie up to a dock before going sailing.
Tying a Hywayman's Hitch
A loop goes through the ring, then from the boat side of the rope another loop is formed and gets slipped into the first loop. From the working end (the left side) another loop is formed and slipped into the second loop. At that point you can tighten the knot and it will hold. I like to add still another loop from the short working end. When you want to until all you need to do is pull on the working end (on the left of the illustrations) and the knot falls off and away you go.
I guess you could release a horse and run away fast if you were a highwayman.
This web site reflects my personal ideas and doesn't represent anyone else's point of view.