The film was underexposed and the pictures came out too dark.
Recent Examples on the WebBright, reflective snow can trick your light meter, causing auto exposure to underexpose and create gray snow.Washington Post, 11 Nov. 2021 Often, if too much bright sky gets into the scene, the camera’s meter will try to prevent it from blowing out and will then underexpose the subject’s face.Popular Science, 27 May 2020