Both Beretta 38 and 42 submachineguns have two triggers. One for semi and the other for full auto. They are not the only examples so designed. They were widely used by German Paratroopers during World War Two.
I'm guessing that's what your friend has.
http://www.forgottenweapons.com/subm...-m1938-family/
http://www.militaryfactory.com/small...allarms_id=126