Just to clear things up, the exception to 370-17(c) still requires that NM cable enters the box through a "cable knockout". From what I can see in the photo, the cable is entering through a conduit knockout.
Redsy's comment was correct..that the exception is more pertinent to the notion that you can staple the unclamped wire within 8", measured along the wire, and an exception to the usual 12" allowed in Article 336.