Actually, that would only be true if the earth was flat. the only way both bullets would hit the ground at the same time would be if the ground extended perfectly parallel to the angle of the shot, which would be perceived as the ground sloping upwards from the perspective of the shooter.
Otherwise, there would be an effective drop off of the level of the ground from the perspective of the fired bullet due to the curvature of the earth (however slight and imperceptible), which would remain in the air for a longer period of time compared to the dropped bullet.