I'm a white guy in Iowa. I am not sensitive to remarks like this, but that doesn't mean it's not potentially offensive to a black guy from Cleveland, especially an extremely successful one.
I've heard the term "posse" used down south of white guys and girls. I don't think of it as a racially charged term. If Jackson said "gang," that would be different, but I've even heard white people call to their "gang" in the scooby-doo type way.
The thing was, I'm not sure Jackson was talking about his business associates. Maybe he was, but it seems like Jackson was talking about Lebron's friends and family (some of which are his associates, but that was not the context in Jackson's mind). In that context, it seems like a normal comment from an old guy who is not really thinking about race at all, but speaking of a group of people in a old-timey way.
If I'm Jackson, I would call James and apologize for being insensitive. I would assure him that he respects James' success as a business man and that he was not belittling his accomplishments.
Even if he says that, Jackson does not have to back off the idea that James wanted to have special treatment from the Miami organization, and that was inappropriate.