Do I understand correctly that their observations are compatible with the possibility that some ethnic groups have more of this phenotype and these ethnic group

Do I understand correctly that their observations are compatible with the possibility that some ethnic groups have more of this phenotype and these ethnic groups are becoming a larger percentage of the world population in general? This would make the story about the artery a red herring. For example if Northern Europeans started reproducing at a higher rate, could we say that humanity is evolving more and more lactose tolerance? I would say that would be very misleading. My question is, does their methodology tell apart the following effects: - The new artery is spreading across the board in various places, e.g. there is a general environmental selection pressure for random mutations in this direction, OR - Populations that have it or don't have it are reproducing at different rates, possibly for totally unrelated reasons like socioeconomic ones.