The "CodeBehind" attribute in the page tag tells visual studio where the code-behind file lives. This attribute is for the convenience of visual studio only.
The "Src" tag tells the ASP.NET engine that you want that ASPX page to compile the referenced file. It does not make any direct link between the file referenced and the file referencing it.
The "Inherits" attribute tells the ASP.NET engine what class the ASPX page should derive from. The desired class can live in the code file referenced by the "Src" file or in any assembly found in the application's \bin folder or in the .NET global assembly cache (that's where System and System.* are found).
If your goal is to "hide" the code files used for the pages just precompile everything so you don't have to distribute the code-behind.