He is talking about C# 5 which does exist as it was released with .net 4.5
As for which book to get, it's difficult to say. I would look at reviews for both and see what people have to say. Keep in mind that neither choice is a wrong choice. I would recommend going for the version 4 book ( it'll probably be cheaper ) unless the newer copy happens to teach it in a better way. You can always use web resources once you've finished learning the features in version 4 to learn version 5 afterwards.
As for Visual Studio versions, you can always use the latest Express Edition which will allow you to use features from the newer version of the language for free at http://www.microsoft.com/visualstudio/eng/products/visual-studio-express-products