No, ethnicities are absolutely not just administrative or cultural groupings. You've clearly done no research into this topic whatsoever and are just repeating some misinformation you got fooled by. Even the classic races which are unnecessarily crude by modern standards do actually partly correspond to distinct genetic groups. We can now classify ethnicities at a much finer level of detail and they're still distinct genetic groups.

Ironically given the article this is under, IQ was considered to be dirty Jewish science by the Nazis, probably because it showed Jews to be superior.