Germany and Austria are next-door neighbors. So it is not surprising that their customs are a bit similar. Like the Germans, many Austrians are Catholic, so they also celebrate All Saints' Day, All Souls' Day and All Souls' Week.
Austrians also believe, as do their German neighbors, that this is the sole time of year that dead souls can return to Earth and visit their old stomping grounds. But rather than worrying that they'll accidentally stab or slit these spirits, Austrians are concerned with making them feel welcome. So they keep their lights on at night, even after they have retired for the evening, so the souls don't have to fumble about in the dark. And since the journey from the netherworld to Earth is likely a tiring one, they also set out some bread and water for these famished and thirsty beings.