Sephardic or Ashkenazi? #dna


Dear friends.
I am new to the group though have been in family research for many years.
I am managing my cousin's family tree research by her request as she is not
so involved in research methods.
Recently I submitted her and her son's DNA sample to the Family Finder in
FamilyTree DNA.
As expected she came as 98% Ashkenazi Jew origin but to our surprise her son
came as 100% Ashkenazi Jew.
Why surprise?
Her late husband family tree goes back to the 16-17 century in Holland and
though the husband paternal grandfather's ancestors are Ashkenazi Jews
mostly >from Germany, clearly some of the branches (e.g. all his paternal
grandmother side and some of his maternal grandparents side) are Sephardic
Jews, going all the way back to Portugal.

My question is, why the Sephardic ancestors do not show in the Family
finder origin.
Is there a better test to pick up the Sephardic origin.
Or - is the family tree known to us - is wrong?

Yohanan Loeffler
Melbourne Australia

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