Contradiction? I think marriage arrangements don't influence things,only the egg has mtDNA.
Indeed--the cytoplasm of the sperm is negligible, so (essentially) all the mtDNA comes from the ova. The contradiction would be why, in this limited area, would there be so much diversity of mtDNA? One way to possibly explain it would be for the dominant males to raid other islands and bring captive women back--women who would have different genetic lines.