Apparently, this particular ROM was picked up courtesy of an error on the website samsung-updates.com as reported on the forum. Needless to say, the entire story does seem to have a fair number of holes that does not hold up upon closer scrutiny at first, although it might just end up as being one of the “hard to believe it, but it is true” stories of the year where leaked ROMs are concerned – since the thread that talked about the incident at length on XDA also has a download link alongside the entire bunch of instructions required for a manual flash.
This is about the real deal – at least on an unofficial basis, and since it is an early beta, do not expect it to run perfectly fine without any kind of kinks or hiccups.