No, Robert Cailliau (the Belgian you are referring to), did not have a part in its invention, he had a part in its development. Cailliau also had a part in writing the proposal for funding, but he did not invent it. Inventing has to do with creating the idea / concept, and development/refinement of the invention is completely separate. Berners-Lee had proposed the idea to CERN before Cailliau was on-board.