That was sweet and fun! I recently learned that the intestinal parasites in fish can tell when the fish has died, and will quickly migrate into the muscle, so they can be ingested by whatever scavenger (or fishing predator) might eat it. Because of this, commercially-caught fish must be chilled in ice, to prevent this migration, trapping many parasites (particularly tapeworm larvae) in the intestines.
By quickly cutting the fish for sashimi, they probably were fast enough to avoid this migration.