While signing up is mentioned several times on their page it doesn't seem to be required in any way to run your own version. I hope the broken download is just a bug. Signing up just so you can download the package would be pretty annoying.
> Open Signup on Ghost.org The most important piece of news, of course, is that Ghost.org is now open for signups from everybody. Get over there, create your account, grab your username, download Ghost, and check out the forums.
The top comment only confirmed my suspicions.