Most teen celebrities that start off with the adorable, clean, sexy-but-not-slutty image have a hard transition to make to adulthood in terms of public appearance. If you don't throw off the clean-cut image of your youth, you will not make the leap. You lose the edge and the aging fans who no longer want to date a 16 year old.
But managing that change in public perception is difficult. I don't think that Lindsey Lohan did a good job, for instance, but she's still around which is better than can be said for many child and teen celebrities.
Justin's got a few rough years ahead of him, and you can be sure his agents and producers are working overtime to make sure some stuff leaks out, but not too much. It would be surprising if this was his first time, and that he did it accidentally in a place where it would be caught.
Still, it might be too early a reveal, and certainly a hard one with a steep cliff, so it may in fact be accidental.