They're a club that's just made their way back to the top in Italy after an enforced exile, and are perhaps, if I'm generous, the biggest of the pretenders to Europe's top table at the moment. They've done nothing in Europe for years, whereas United have been in three finals over the last five or six years.
They're easily a step down from United at the moment, if not more than one (i.e. several) steps down.
Obviously I wouldn't put all my money on United beating them if we came up against them, but I wouldn't be putting all my money on United beating Cluj in our next CL game either. It means nothing.