Not saying you are wrong, but I did look up "belt fed assault rifle" out of curiosity, and found a few interesting results. The old FG 42, considered a fairly state-of-the-art gun for its time, is described as a rifle weapon with compact machine gun characteristics. There's also the ARES belt fed rifle, and a number of tacticool-esque upgrade kits for belt fed AR-15s.
I saw one picture that was apparently an AR-15 with a reduced barrel, pistol grip, and a bullet belt conversion that turned out more like a belt fed submachine gun (I thought it looked a little silly).
Just interesting to note that the ammo type, weight, and size don't always seem to classify a weapon as a machine gun.