That looks like a failure of the Boeing C duct. Not unusual.
We had one here in ARN on MH about 4 years ago, and BA had one out of SIN two years ago. The C duct is composite, covered in heat shielding blankets. If the heat gets between the blankets, the duct disintegrates.
The MH one I had here had an awful lot more C duct missing.
I wonder how the crew noticed?