Yes but that is due to the vastly different population density.

The USA has 34 people per square km while Germany has 234. So pollution per capita would be a better metric.

The air you breathe is the same regardless of how many people stand next to you also breathing it.

But only if they stand.

If they start driving, the situation changes dramatically!

Actually if you're standing next to people the air you breathe in also has some of their exhaust gases in it, in this case slightly elevated CO2. If there's a dozen people in a small meeting room with the windows closed and no AC the air quality is significantly worse in that room than it would be say, stood on the roof... unless you're in the middle of a major city where maybe the air on the roof is full of exhaust from motor vehicles, hence legislation to restrict vehicle exhaust.

The average air quality in all of the US is not as bad as in some European countries?

Most. Not some. Reading comprehension is important. Don't they teach that in Switzerland?

You compare a continent to countries? Without any corrections for density or anything? And you ask me about my comprehension skills?

Air in populated cities or air in general? Air quality seems a bit harder to compare across countries than road deaths, considering the US has so much sparsely populated land.