The term has been attributed to Josh Sugarmann, head of the gun control advocacy group the Violence Policy Center. Going by this quote of his, he likely came up

The term has been attributed to Josh Sugarmann, head of the gun control advocacy group the Violence Policy Center. Going by this quote of his, he likely came up with it to intentionally confuse people who aren't knowledgeable about firearms. "The semi-automatic weapons' menacing looks, coupled with the public's confusion over fully automatic machine guns versus semi-automatic assault weapons — anything that looks like a machine gun is assumed to be a machine gun — can only increase that chance of public support for restrictions on these weapons."