It bothers him that so many people don't get that the film version of Coraline was directed by Henry Selick. People who aren't paying attention (or, apparently, thinking) see the Coraline ads saying "From the director of The Nightmare Before Christmas" -- and somehow miss that some of those ads also name-check Selick -- and think the film has something to do with Tim Burton, when it has nothing to do with him.* (Even that TV Guide TV channel with the cable listings scrolling by have commented on how people keep doing that, and have added that nope, it's Selick's baby.) And Neil's been trying to correct that misperception. And this has resulted in stuff that's funny, like this.
Me, I wouldn't want to make Neil Gaiman grumpy, partly because I don't like pissing people off and partly because I wonder if Neil Gaiman is like me and wants to say Please, people, it's not that hard to keep straight if you just pay attention. But here's what I admire: even as he's annoyed, he's making good, relevent points. Sometimes -- and I know I can do this -- grumpiness short-circuits the thought process. Thoughts are likely to be bitten off and flung, and not necessarily the most pertinent or fair thoughts, either.
But Neil does seem to admit it when he's grumpy and annoyed, while still showing his well-thought-out thought process. He's a careful thinker and writer (sometimes, I think, too careful a writer; I want him to cut loose with insanity more often like the dive-bombing flamingoes** of Anansi Boys), and he remains careful when annoyed. Just remember, people, how maddening it is when people don't pay attention to what you're saying. Another recipe for grumpiness.
*I've heard of problems like this before. Terry Gilliam got better known through Monty Python, then after a less-than-satisfying experience directing a Python film (when he and Terry Jones co-directed Monty Python and the Holy Grail) he decided to direct only his own movies. His first was Jabberwocky. Some people called it Monty Python's Jabberwocky when it wasn't; at least one theater reportedly listed it as, bogglingly, Jabberwocky and the Holy Grail. Even an official VHS release years later of the film called it Monty Python's Jabberwocky, no doubt to Gilliam's annoyance. At least he avoided that with his later films; no one's going to think the sadly gentle and lovely Twelve Monkeys is a Python film.
** "Dive-Bombing Flamingoes" should be a band name.