I think that's it. The e-cigarrette acted like a primitive "cannon" with the exploding battery propelling pieces of the cigarette holder into the kid's mouth.
Then there’d be far more damage to the soft tissue of his chin and lips. The “cannon” scenario is inconsistent with the injuries which are mostly internal, not external. Even it an explosion occurred internally, much more soft tissue should have been blown out than is described!
The mass of an e-cig is on the wrong end for the physics to work. The plastic walls of the “cannon’s” barrel would fail before any pressure could possibly build to propel the mass with enough force to break a mandible, one of the strongest bones in the human body. . . and, once again, Lithium Ion batteries do not “explode, regardless of what breathless hyped news accounts claim; they expand, heat up, conflagrate, and, at worst, burst into hot, rapid flames. They are not an explosive. They do not put out high pressures.
Instead, the damage seems to be from something hitting him as if the lips were out of the way. His chin was swollen but not cut when the doctors saw him. That was from the broken jaw. Take your finger and put it on your the top of your lower teeth in the middle and move it down one-half to three-quarters of an inch, a good way below the top edge of your gums, and move it over a bit to the right of the center line. That’s the center of the force of the impact that broke his mandible and center lower teeth roots. No damage was done to his upper teeth at all. No damage to his chin or lips, except a lip minor burn. Yet the treating doctors described the mandible injury as what he’d expect to have been from a “car accident”. That’s a lot of force! That is not the signature of what was described by him. No “explosion”. No “cannon”.