What is this design pattern called where methods are instance methods and not class methods?

 NSData *_dataArchive = [[NSUserDefaults standardUserDefaults] 
                                        objectForKey:@"Session"];

This style is pretty common in Obj-C.

Why is it [[NSUserDefaults standardUserDefaults] someMethod]? Here someMethod is InstanceMethod?

Why not [NSUserDefaults someMethod]? here someMethod is Class method.