Watching the fight and taking BJs word for it, he injured himself taking Matt's back. As you watch, you can see that he really bends himself very awkwardly taking his back, so it seems like a legit pull to me, and one caused by himself moreso than Matt. Like I said...I still give him credit for surviving the first two rounds (albeit barely in the second round ) and being able to capitalize on BJs injury. BJ injured could probably still wipe out the majority of the UFC WW division.