What if it is a short bus? It's half the size of a bus, yet still a whole bus. The joys of fractions. Half of a short bus would be a passenger van. Still a bus? Half of a passenger van would be a mini-van. Half a mini-van would be a SUV. Half an SUV would be a sedan. Half a sedan would be a mini. Half a mini would be a bicycle. Half a bicycle would be a unicycle. Half a uni would be...
No, the… the point is encountering something upsetting is upsetting, but encountering it not intact is traumatic.
Half a human swallowed by a whale is body parts. Half a worm in an apple is half a worm in your mouth. Half a bus hitting you implies more than the bus/human collision and some prior trauma experienced by the people in the bus.