I learned through similar bad experiences that the key to communication is to speak their language. Describe things in terms of their frame of reference and do not assume that they know anything about your technical frame of reference, unless you know for a fact that they do.

The problem here was that Frank did not understand how far a mock up or prototype was from the finished product. In his mind the detailed design, programming and testing was probably little more than editing a rough draft. To an engineer or an architect, describe the prototype as an initial drawing. To a business person, describe it as a "straw man" process model. They'll understand that most of the work remains to be done.