By the BATF's definition, would not most double-barrel shotguns qualify as machine guns? After all, by their definition, something that can be readily modified to be a machine gun is a machine gun, and most double-barrel shotguns could easily be so modified (e.g. two-trigger models could be made to fire twice with one trigger pull by simply fastening the triggers together).
I doubt they try that, but on semi autos especially those in military style, I can see them landing on someone hard. In light of post 14 though he may actually have been in possession of a modified weapon. Also, the quote I posted was from another article and may not be what the government argued.