If we open a debug workflow we can see exactly what is going on 'under the hood' if we run this as if we're selecting an Excel file - the .txt container is disabled and therefore nothing comes out of that into the union - we just get the Excel data:
If we open a debug workflow we can see exactly what is going on 'under the hood' if we run this as if we're selecting an Excel file - the .txt container is disabled and therefore nothing comes out of that into the union - we just get the Excel data: