This is really not that rare in Europe. There are many hundreds of historical cities with large sections built before cars. Pedestrianized zones are popular and even where cars are present, there's a much better balance between pedestrians and cars. Overtourism is also a very localized phenomenon. The vast majority of people never wander beyond a single square or a single high street, as is mentioned by the author when they say they go one street back.
The lesson is that if you go to a globally famous city during a famous festival, and stand in a famous square, you may find quite a lot of other people with you.
I traveled around Europe while living in Munich and that wasn't quite my experience.
Yes, there were many places that were highly walkable or pedestrianized city centers, but sizable cities where cars didn't exist in essentially the whole area? I didn't see that, and so far the specific examples people have mentioned have been small towns or just city centers with no cars.
I suppose you could call Venice that, but you could also see it as a historical district of the larger metropolitan area. The metro area has a population of 2.5 million. Only 50k live in Venice proper.
The lesson is that if you go to a globally famous city during a famous festival, and stand in a famous square, you may find quite a lot of other people with you.