Why even acknowledge the passenger? You're addressing the driver's actions even though you stated it was the passenger who was directing you to go ahead. Unless you're inside the vehicle there's no way you can know if the passenger is communicating what they're doing to the driver, or vice-versa. Whether I was on a bike, in a car, or on foot, I wouldn't heed any direction from anyone within a vehicle other than the driver who is controlling the vehicle.