Bubble-bursting time. Sorry folks (and calm down, mo!
), but the download link can be changed by anyone in the addon files. I could take an addon and have the download link specify
www.neogaf.com, for example. Also worth mentioning is that the tutorial addon's (Dead Line) download link is on the steam store, and its addon files are often used as a template by third party mod makers. It's very possible this is the work of fans.
The original L4D1 campaigns ARE coming to L4D2, it's just anyone's guess if Valve or the modders will do it (bet on the modders, they're eager and Valve's supplying the tools).