Sure, I can see how some could interpret it as an asshole move, but certainly not one that requires them being put in their place. They bought a ticket to an entertainment event; they shouldn't be heckled for that.
What's more asshole-ish: wearing another team's gear to a sporting event, or heckling someone for nothing more than wearing another team's gear to a sporting event? I know where I cast my vote.
Hell, we as Husker fans pride ourselves in the fact that we travel well (we keep throwing up a picture of a Notre Dame football game from 15 years ago to pat ourselves on the back). If the logic is that people who wear other team's gear to a sporting event are assholes, then for a couple decades Husker fans were the biggest assholes in sports.