By visual prototype I mean: not working. The screen graphics on that prototype are likely paper with printed pixels and a sheet of polycarbonate stuck over the top. All very simple methods to make something that looks right, but certainly doesn't do anything useful. Its a very common process[0] in industrial design. The housing mouldings are made from polyurethane cast in silicone moulds (vacuum casting).

I am a product designer (physical products)

[0] http://www.amalgam-models.co.uk/services/prototyping/