I thought this made sense:
?Gaiman began the novel as a short story to explain himself to his new wife, musician Amanda Palmer, who was away recording an album. But as he wrote, the story took on a life of its own. (and any Gaiman fans must google 'Amanda Palmer Daily Mail video', if you do not know about this already as she is amazing, thread about it on MN :))
?I?d get up every day and go, ?Well, it?s got to be finished by the end of the week, hasn?t it?? And then the end of the week would happen and I was going, ?Well, it?s not a short story, it?s obviously a novelette,? and then I thought, ?Well, it?s not a novelette, it must be a novella,? and I did a word count and I went, ?Bloody hell, this thing?s 56,000 words, that?s a novel. Not a long novel, but it?s a novel.???