He's cheering for the Red Wings. The Red Wings! The audacity!
Tonight is an extremely important game for the Philadelphia Flyers, in case you haven't heard. The Flyers, Red Wings, and even Bruins are all neck-in-neck for the two final playoff spots in the Eastern Conference - so a match-up between two of said teams is huge.
Naturally, all good-hearted people are cheering for the Flyers. Then, there's The Walking Dead's Steven Yeun.
Now, this isn't entirely his fault - the actor who plays the very likeable Glenn grew up in Detroit.