The Wing to Body fairing is a Honeycomb Fibreglass fairing attached to the Fuselage by screws, not bonded to the skin. If it failed it would not damage the Aircraft skin.
The Passenger Oxygen bottles are in that area of the Freight bay but i think the last one is in the area just in front of the hole, if you look closely at the pic you can see the rear edge of the velcro'd curtain that covers them. Also as all Passenger Oxygen bottles are connected to each other, if one bottle blew then I think all Passenger Oxygen pressure would be lost, but not entirely sure! The fact that all Passengers had oxygen I think rules that out.
- 747 Engineer