That somebody had simply taken the bag from the cardboard box it was sold in, for some reason (maybe space). These are called cubi in France (from cubitainer)

That somebody had simply taken the bag from the cardboard box it was sold in, for some reason (maybe space). These are called cubi in France (from cubitainer) and used to be hard plastic containers but have been bags in cardboard boxes for maybe the last 30 years or so. They have a reputation for being used for the cheapest wine possible (which was likely the case if you were students) but can also be used for better wine, it's actually a rather good storage device as it still excludes oxygen once open unlike regular bottles.