The mistake lies in the fact that the object index is always 0, so you will not get more than one object based on that example.
// Search through the FBX scene to find our custom objects
int Iter, Count = pFbxScene->GetSrcObjectCount<MyCustomObject>( );
for ( Iter = 0; Iter < Count; ++Iter )
MyCustomObject* MyCustomObjectInstance = FbxCast<MyCustomObject>( pFbxScene->GetSrcObject<MyCustomObject>( 0 ) );
// REPLACE 0 with Iter
Mistake in FBXExtension sample in OR SDK