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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.

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