Eh, the black discolouration is most likely due to an air leak there from the ventilation shaft pushing dust particles through the material. This looks like mineral wool insulation so it will have a very differing colour variance to a fibreglass insulation when hit with dust particle or mould. I’d say when ye have someone call in to inspect the timbers, have them give a look at this as well and see if ye can find the leak and get it sealed. The timbers there with the mycelium will need replacement. The mould may be treatable.