When a .TWBX file icon is double clicked, The most recent Tableau product that was downloaded to the machine attempts to open the file. In this case, Tableau Public was the most recent download and is attempting to display the file which does not exist on Tableau Public.
In order to open and view the .TWBX file, it will need to be opened using Tableau Desktop. This can be accomplished by either dragging the .TWBX icon and dropping it on top of the Tableau Desktop icon, or open Tableau desktop first and click 'File' then 'Open' and navigate to the desired file.
In order to make Tableau Desktop the default application for opening .TWBX files on double click, please download the most recent update for Tableau Desktop.
The updated release may be downloaded from the link for 'Alternate Download Site' in the Customer Portal: