They claimed that the difference was mainly due to lifestyle. People in the city tended to travel more by plane

So, again, this seems like an inequality issue, if only wealthier people can live in cities, cities will reflect the habits of the wealthy.

I suspect that those who take the bus in this particular city are those who would’ve otherwise biked

Biking is something you can largely only do in metropolitan areas, lord knows it's suicide to try and commute daily on the side of a road with no infrastructure for it.

You can easily go out to consume and thus cause emissions. When living in the countryside, you can walk to the closest lake and fish your dinner without any emissions

Weird strawman, you know cities have parks, right? And cultural centers like museums that are often free for residents, local theaters, etc, none of which you would need to drive to.

Pretending that cities is the most environmentally friendly place to live is to ignore what people do except working, sleeping and traveling between the two.

Except the more people you have, the less infrastructure and emissions are required per person; there is a built-in efficiency. If you could click a link and read, instead of just assuming your preconceived feelings are true, you could have learned that "When the size of a city doubles, its material infrastructure—anything from the number of gas stations to the total length of its pipes, roads or electrical wires—does not. Instead these quantities rise more slowly than population size: a city of eight million typically needs 15 percent less of the same infrastructure than do two cities of four million each."

Cities are where people are, and its cheaper and more efficient to do things where people are, simple as.