If you have population of 1000 with birthrate of 20 per 1000. You get 20 kids.

If you have population of 2000 with birthrate of 16 per 1000. You get 32 kids.

This is just an example, but effectively birthrate can go down while at the same time absolute number of births goes up.

At the same time there is a global trend that populations are concentrating in Urban areas.

For example in the US 80% of the population lives in Urban areas and US Census Bureau only considers 3% of the country's land area Urban.

Also depending on which country you are from immigration can compensate for falling birthrate.