Not familiar with the 747, but on the 737-700 I fly (and don't ask me why....) I paid particular attention to the equivalent fairings on my last walk-round. They're placarded with the words: 'Caution: ensure fasteners used are of correct length'.
If a lazy engineer jammed in a fastener that was too long because it was a long walk to get the correct replacement from stores, is it possible that it could have been left contacting the skin beneath. Then with abrasion over a period of time, could a weak spot have developed that eventually failed explosively under pressurisation, ripping a big hole?