You underestimate marketing in general. Big companies have marketing departments filled with very intelligent, highly-paid people to do just this kind of thing, and they are quite literally masters of manipulation, in that they studied sociology and psychology at degree level. The "iPhone in a bar", deliberate-leak type marketing is just scratching the surface. Almost nothing is as it seems.
From what I gathered it was legitimate mistake. It was iphone4 put in a 3gs shell to hide it, some random guy found it quickly found it out it was a prototype and decided to sell it in order to make a quick buck.