Not to scratch my head too much but that's a big, not heavy, dog.
The neighbor saw the carrier jerk up the dog and throw it up in the air? Something weird in the story. I could see a carrier coming into the yard and kicking, hitting or dragging the dog. Somebody looking to do something mean to a dog would not get the dogs teeth anywhere near their neck.
As an addition. Both of my dogs are about that size and they are some wiggly critters to try and snag hold of and pick up.