Curious myself, so answer nicked from another site.
The A330 normally has a slight nose down attitude when on the tarmac. Not a problem for passengers, but a bugger when you are handling freight apparently. So the solution is rather than a longer nosewheel strut, to move the mounting point lower for the existing nosewheel, unfortunately that means that it no longer retracts to be flush with the existing airframe - hence the bulged fairing. The quoted height of the freighter is .50cm lower (same tail same fuselage length as the A330-200) due to the fuselage being level.