Not all MZs are ribbed, and some generic Egyptians are. Sometimes it's really difficult to ascertain whether or not a rig is an MZ knock-off. If it still has the black rubber base grommet, wet it and pull it off and take a look at it. Usually, even if the original tray has been replaced, the original base grommet will bear the Magdy Zidan name on the lip.
Either way it seems like you got a great deal and if it smokes well then that's all that matters.