You haven't studied history, It is well known that the vikings
brought many Irish slaves with them to Iceland. This study is bogus,
because the people of northern Scotland are actually mostly of viking
decent.
Linguistics is one field. Genetics is another field. History is yet
another. When people in one field pretend to be experts in a different
field they make major blunders.
http://www.delphi.com/nordichistory1
http://www.delphi.com/paleogenetics1