Bonding?
Can't remember the exact type of material used for the forward wing-box fairing, but a little bell is ringing back there whispering it's a carbon-carbon reinforced, or carbon-reinforced fibreglass moulded section that is fitted aided by gravity in that the section "latches" onto retaining studs in the fuselage section, "hung" there and fitted, then the entire contact section bonded to the fuselage using epoxy and ultra-violet or infra-red heating to ensure the strongest possible bond betweene the two segments, prior, of course, to being spray-painted.
That particular area, together with, for example, radome hinge-joint areas and the lower sections of forward-facing cockpit window installations, have throughout the history of aviation been known blackspots for moisture intrusion... Wing box fairings aft are particularly susceptible to contact with ramp handling equipment (witness for example the number of A319 ULD-equipped incidents with Spanish-designed purpose-built "high"-loaders smashing serenely into the box), however the forward or leading-edge section of said wing-box fairing has an extrememly important function ensuring undisturbed airflow around the wing-root, over both the wing surfaces, along the fuselage and toward the tail section.
In this particular case, we do not yet know if it was an explosive decompression or if the incident was a result of a fatigue-induced "peel-away" of the bonded surfaces. In either case, the aircraft seems to have come off relatively unscathed; a blow-out would concievably have propelled detritis into Eng 3 and possibly Eng 4, the result of which would not make for bedtime reading.
It'll be interesting to follow this case through: the literature eagerly surrenders several seemingly similar cases, the most spectacular of which was the unintentional invetion of the B737 open-top Hawaii tourer.
God Speed.