I've only lived in stone or concrete houses, there has always been enough of a gap between the drywall and the house walls to expand mollies into. That air helps noise and heat insulation, as well as being useful for passing heating water, electrics etc

Well the concrete houses I lived in never had drywall on the wall at all :). It really depends :)

So raw concrete inside? and they painted directly on it? o_O

Concrete or more typically some kind of (concrete) brick, then plaster, then wallpaper, then paint.

At least in many German houses.

well that's drywall no? the sheets of plaster between the wall and the wallpaper

Plaster can be very thin and it isn't sandwiched between sheets of wallpaper. It's used to smooth out the wall texture.

You can also have concrete wall with plaster and then on top of it paint, no wallpaper at all.

Standard way to build here for the last 50 years. Indoors, the raw brick or concrete wall has a thin layer of "flattener" plaster spread. No drywall pieces.

Most of the time no wallpaper.

Presumably they mean just plaster, not sheets of plaster board.

exactly ;)

Raw Beton or plaster on brick/beton with or without wallpaper. Paint on top. So many variants :)

wow I've only ever seen that in very old houses before renovation

Where I live the walls are brick and then you plaster on top of them.