To kill quickly, the peice would have had to have blocked the airway. Even for a large 10' snake, that opening is quite small. I would think that either it was some sort of freak accident OR the snake had so much bedding packed in its mouth that it somehow was forced to inhale solid dirt. Bizarre story.
My biggest beef with paper is that you can't really spot-clean it and anything like a large uriniation over water-dsh overflow creates an unhealthy mess. On the other hand, with an inch of coco mulch your snake could completely unload itself and then go and tip over its water dish and still find a nice dry place to coil up.