The relation of carrier and passenger persists even after passenger alights from vehicle

Dear PAO,

Last Sunday, JE and his family took a bus from Cubao to Sta. Cruz, Laguna. Upon reaching their destination, they disembarked, but JE returned to get their baggage. Unbeknownst to him, his youngest son followed. When JE attempted to re-enter the bus, it accelerated, resulting in his son's tragic death. The bus company claims it is not liable because JE's son was no longer a passenger on the said bus. Are they correct?