What about the Judge causes this that doesn't happen in a traditional .410 shotgun? Or does it?
That's a good question. They were using standard buck, not Judge-designed.
I wonder if the first ball gets a little drag when it hits the rifling, just enough to allow the free-boring second pellet behind it to catch up and mush, which then snags even more of the rifling slowing it down even more, which results in third pellet hitting it even harder.