I don't think there is a chance in the world that Christie would intentionally call a black man "Boy" in front of an audience and a camera, or even in private.
On the other hand, even using the word "Boy" in a questionable context with blacks present is quite a mistake for a politician to make. Most politicians don't use the word "Boy" at all around blacks. Mistakes like this will sink Christie.
Interesting to note off topic that it now seems to have become acceptable for blacks to refer to young white males as "White Boy." Just not the other way around.