Cargo fire or O2 bottle let go?
Hmmmmm....
There are 2 horizontally mounted crew oxygen bottles just fwd of the "hole" in the fuse. By the looks of it, the hole is around the area where the first of the vertically mounted pax oxygen bottles are located, along with some flow control regulators. As stated by clipped, there are also cargo fire bottles in this area.
When I saw the pic for the first time, I instinctively thought oxygen due to the location. It will be interesting to see what the investigation findings are. In any case, hats off to the crew and pax for an injury free safe landing.