The article says that it was first posted on Reddit, but nobody noticed for a while. The Github copy is almost certainly a repost, by a different author than the original leak.

"This source code first surfaced last year, posted by a Reddit user called “apple_internals” on the Jailbreak subreddit. That post didn’t get much attention since the user was new and didn’t have enough Reddit karma; the post was quickly buried. Its new availability on GitHub..."

There’s lots of stolen shit on github, including (as of a few months ago) the Windows 2k3 kernel.

I’m not surprised by this leak. I am surprised more people aren’t aware of this.