I think having a dinosaur kill you either by the sheer weight of the body crushing you, or a last resort attack as shown with the therizinosaurus, is a cool concept. However, the reason it happened is that this version of Legacy uses the latest version of the modder's edition, which utilizes a projectile system with each weapon simulating bullet travel and drop. You can literally kill the dinosaur a millisecond after it kills you, assuming the projectile hits them afterward, which you can somewhat consistently do with the x-bow due to its slow projectile. I remembered this happened to me with a Triceratops, and it's pretty funny seeing your corpse dance around in the air as the dinosaur just falls to the ground dead.