The page only lists 126 cities, with the bottom three having an AQI of 0.

So the editorialized title is incorrect. It's not "top 5 worst air quality worldwide", it's only top 5 in this list, which is a small subset of the world's cities.

It's a Swiss company but even Switzerland's largest city, Zürich, is missing.

China sure as hell has more than 8 cities and Russia more than 2.