It came as a surprise to me
after over 20 years of seeing “normal” world maps
to come across an upside down one.

The most surprising thing was that I found it surprising.
It is completely artificial that we have North at the top of a map.

The convention came a few centuries ago
when Northern hemisphere, European navigators
started using the North star and the magnetic compass.

Before that, the top of the map was to the East
which is where the word orientation comes from.