The article suggests they are German, not Swiss. But indeed both countries have a low birth rate, as do virtually all developed countries, you are correct. However as you also point out, migration tends to send people from the countries that have high birth rates to those that have low birth rates, largely because those countries simply cannot sustain them, largely due to war and poverty (sometimes brought on by overpopulation and lack of resources). So high birth rates in other countries become a problem for everybody. Even the United States, with a birthrate of only 1.88, is experiencing steady population growth thanks to high birth rates in developing countries. By saying their home country could use more people you are basically saying overpopulation is a localized problem, but it's clearly not.