Active directory for .net application

In a C#.net 2008 desktop solution I am working on, I would like to know the following;
1. When an application starts and it knows you (as the user) by domain name/username, is that application using the active directory?
2.  In this solution I find code that looks like the following:
System.Security.Principal.WindowsIdentity.GetCurrent().Name.
 Is this application using active directory? If not, can you tell me the type of credentials that are being used?