Or it was, as is common in many kitchens and bathrooms but also living rooms, a vinyl wallpaper. No mold can get through that, but the paste is a great breeding ground.
The condition of the windows is a stronger alarm signal for me. It takes a lot of persistent moisture, pest infestation, and complete neglect for a window to look like that. That leaves little hope for the roof truss, the floors, ceilings, and the masonry. With this type of construction, deteriorated sewage pipes would not surprise me either.