What he means is if he has a toy helicopter hovering in a stationary car and then the car pulls away, the helicopter will appear to the occupants to travel to the rear of the car and hit the rear window.
That's not same as you jumping vertically upwards while on a bus travelling at 50mph. If you jumped vertically upwards in a stationary bus, just as it pulls away, yes you would land further down the bus because you were both initially at rest and while you were in the air the bus moved relative to you.