Not completely true. Guns of a "military caliber" are illegal for civilians. That's why 1911s chambered for .38 Super are or were so popular there. Rifles in non military calibers and of course shotguns are legal, if controlled.
Still that M-1 Carbine is not only a military caliber, it's a military rifle. (Looks more or less like mine, including the shade of the stock. Imagine that. :) )
Which would also be the sort of cast off weapon one might expect small city in the "boonies" police to have.