Yes, genetics likely plays a part. However, it would matter more about protein during early years, than average across the whole population. Once people are fully grown, it wouldn’t matter so much any more. American diets tend to be higher in fats and refined sugars, so,perhaps that makes a difference but emricans are also at the higher end of the table, despite having a more diverse population, including races that are stereotypically shorter.

I live in Australia and I know that here they have to use different graphs for different races for babies for normal height and weight. The most common European descent population is shorter and less sticky than the Pacific Islander populations and taller and more stocky than the Asian population.