Here's an article I found on the subject. I agree with the customized jersey theory.
Has LeBron James traded in his beloved Dallas Cowboys for the Kansas City Chiefs?
Following the Miami Heat’s 122-103 win over the Sacramento Kings on Friday night, James was seen wearing a Chiefs jersey under his blazer. Not only was this an especially odd fashion statement — I mean have you ever seen someone wear a football jersey under a fancy jacket? — but James’ jersey had the No. 6 on it to match his basketball jersey number. That means LeBron either had a customized Chiefs jersey, or he is the world’s biggest Ryan Succop fan.
What’s interesting is this isn’t the first time James has shown the Chiefs some love. Two months ago, LeBron shouted out Andy Reid and KC over Twitter:
Kansas City what's good! Can't wait to see y'all tonight at the Arena. Let's go! And S/O Andy Reid and the Chiefs. #HeatlesAreHere