I call those particular things paperweights... and that particular item is not even necessarily a sub-machine gun.. 95% of them are semi-auto (And jam every other shot.)
To be accurate, a machine gun is something like an M-60 or larger, generally considered to be crew served (unless you are Rambo) Usually belt fed and tripod mounted or even more permanently mounted on a pintle .
Stop that kind of talk - I end up going off into dreamland. Belt fed.........mmmmmmmmmmmm..........
Legally, a machine gun is any firearm that fires more than one round with a single pull of the trigger. That would include submachine guns, machine pistols, assault rifles (IE. M-16/AK-47 (real ones), battle rifles (M-14, G-3, FN/FAL, etc) and the larger crew served or vehicle mounted weapons you are referring to.