The application icon is not part of the application object source, it is located in a binary only object within the library containing the application object.
I added a feature request to change this.
Everyone knows that when you save an object, there are source and compiled versions of the object stored in the library. Internally the library format stores the source and compiled code separately. If your application object is called 'myapp', the internal name of the source is myapp.sra and the compiled code is called myapp.apl. Similarly a window called w_main has source with an internal name of w_main.srw and compiled code called w_main.win. The application painter stores the application icon and default fonts in a binary only object called <appname>.pra, myapp.pra in this example.
There are no ORCA functions to work with the pra object so external compilers cannot get the icon name.