What did the author consider to be surprising and significant about the roster of the Canadian hockey team(2007medicine that tigers)?

Gladwell then presents the 2007 Medicine Hat Tigers roster and introduces, in light of this information, observations made by Canadian psychologist Roger Barnsley. While looking over a hockey roster for the Lethbridge Broncos, Barnsley and his wife discovered that most of the players were born in the same few months. The Tigers roster exhibited exactly the same tendency. Most of the players were born early in the year, in January, February, or March.