We are Bears fans.
Ben's godmother is a Packers fan.
She buys him one of each of things so that "he can decide for himself who to cheer for when he's older." It's a nice thought, but since she lives in Wisconsin and he'll be spending every Sunday of football season of his life rooting for the Bears she's probably gonna lose this one.
So that, dear commenters, is why Ben was wearing a Packers fan while he was playing outside.