...but, oddly enough, not "correct horse battery staple" (at least, that's how I'm used to writing passphrases; I guess the comic could be interpreted either way.)

I find that message misleading. The xkcd comic does have a point, and thus should be taken seriously. (Despite the obvious downside that those passwords take longer to type, which is why I still prefer short, cryptic passwords.)

So a better message might be:

"Don't follow the webcomic too closely. :)"

It actually says, "Woah there, don't take advice from a web-comic too literally!"

Its saying dont use that particular password. Any attacker of this script would know what it was inspired by and attempt that password in a dictionary.

Rendering it about as useless as 123456789 in this instance