As it turns out, the jersey was a character back story quirk that was never actually revealed in the movie.
Asked about the choice by MEL magazine, Cameron actor Alan Ruck said: “Since I didn’t grow up in Chicago, I never gave it a thought.
[He] had decided that Cameron had a horrible relationship with his father, but a great relationship with his grandfather, who lived in Detroit and would take Cameron to Red Wings games.
Cameron’s beloathed dad was presumably a Blackhawks fan, so his jersey was a little hint of defiance.