I'm a writer. When we write fiction we agonize over every word then we hand it over to an editor who does the same thing.

When we write a tweet, we don't. Polished prose like Gaiman's doesn't naturally flow straight from the writer's head and first drafts, even from experienced writers, can be quite sucky. So, I do believe this is from him. None of us carefully edit our tweets (or, for that matter, our Medium comments).