Personally, I think Gruger just felt like drawing a cool figure in flowing robes. Look at how much fun he had with these pictures:
Another illustration from the same story:
I don't have all of the originals from the story to scan (The two above came from our friends at Taraba Illustration Art ) but if you look at the following printed versions from the Post, you can get a sense for how Gruger drew each wraith distinctively, each with its separate dramatic flourish:
These are not your run-of-the-mill Halloween ghosts. Here you are seeing Gruger's vivid imagination in action.