Kobe yelled a slur to the ref when the action was directed at him. Publication does not depend on camera shot. He yelled it people heard it and it would have been reported.
Hibbert was doing an interview and he mumbled something that many would not even understand if he had not apologized.
Just like the LeBron video in this thread you can barely hear what this players are saying when they say that phrase.
I don't know. I see what Kobe did as the equivalent of a "hot mic". Hibbert's was a statement given to the media.
The content of Kobe's statement was worse, and it was directed at a ref, which makes it more serious from where the NBA stands. In terms of the public nature, though, I think that statements that weren't meant for public conception should be treated differently.