The Phillips DNA Project

Here is a link to an article about the possible practice of polygyny (a man mating with many women) in Ireland and Wales.  Polygyny is the British word for polygamy.  The author of this article, Dr. J. S. Plant, is trying to explain a populous surname that appears to descend from a single man based on yDNA analysis.  However, it seems to me polygyny could also explain the large number of matches between men who have different last names in Ireland and Wales.  What do you think?