You have a valid and sound question. Count me as among those that got a HUGE percentage of Scandinavian with none in my tree. Meanwhile I have a very heavy population of French Ancestry which didn't show up at all. Some have questioned if "Southern European" could actually be representing French when they too expected some and got none but did get "SE" with no connections to Italy, Spain or Portugal. That has yet to be answered. For me I also have a segment that came back as Southern Asian - I have NO CLUE where that came from!
I did suggest through the BETA button that there should be a forum for questions and answers with the actual Genetic experts.