I think cavity wall as for brick was invented decades into
the last century so you are right.

Not so. My parent's house has partly cavity walls and it was built around
1890. The walls change construction all the way up.

Lower ground floor: Single outer skin, cavity, double inner skin.
Upper ground: Triple brick solid.
2nd/3rd floor: Double brick solid.

Inside you can actually see where the construction changes, because on the
stairs, there will be a useful full length shelf between floor levels, or a
less than neatly rendered "ramp". The exterior of the house shows no sign,
except the deepness of the window frames.

The house is built on a steepish slope such that the back door is on the
lower ground floor, with steps down to the ground level, whilst the front
door is on the upper ground floor level with the street. I presume the
cavity wall was required to ensure lack of damp in the lower ground floor,
which is a proper full height floor, not a cellar, despite being buried at
the front. There is an additional cellar underneath! It appears that the
Victorian builders saw no point in the cavity above rising damp level.
Presumably they hadn't invented cavity insulation by then. The house is
essentially dry throughout, except for occasional guttering or roofing
problems.

Christian.