Obviously, a moon dog is a slang term for a werewolf or someone who surfs at night.
Another reference to Moondoggie is in the Gidget series.
The origin of the Moondoggie in my book, Valley V, might be found in the biography of Louis Thomas “Moondog” Hardin Jr. (1916–1999), where writers mention how he came to adopt his nickname. But it is likely that wolf moved down to Missouri from Pennsylvania, Ohio or possibly over from South Carolina.
One could also say that Moon Dogs worshiped the moon, while Sun Dogs worshiped the sun.
As popular myth tells us, witches, werewolves, and vampires were creatures of the night. Their way was lit by the moon and witches even worshiped the moon. While humans grew their crops with the sun and usually lived/worked only during the day.
But it is also interesting that the natural phenomena known as sun dogs is also known as a mock sun, while the moon dog is a mock moon. This means it looks like sunlight or moonlight but actually isn’t. Could this be the nickname for someone trying to look like they shine or have supernatural powers when they actually don’t?
For surfers, while the sun makes surfing fun and warm, it is the moon that affects the tides.
With a possible reference to the vampyre-related Black Swans, there is a company that has developed lights for surfing at night.