You see the overrepresentation of overseas immigrants’ children in so many areas of achievement. I say “overseas” rather than intra-continental immigration because there are a lot stricter controls on who is able to enter and stay in the country, so the parents tend to be well educated and ambitious to provide a better life for their children. Most of the top American tennis and chess players are from immigrant families. Even going way back to Sampras, Agassi, and Chang who were all sons of immigrants. Second generation Asians and Nigerians are way more educated than your average American.
Maybe there is some genetic difference that predisposes Balkans to be better basketball players than Scandinavians, but both populations are quite tall and have achieved outsized success in many other competitive sports.