It was because of correct sunlight direction and
good sunlight condition. Correct sunlight direction means
that the direction of sun shines on the direction of the bus.
Good sunlight condition means that the sunlight is strong and not
covered by clouds for that particular day.
Examples of shots that oppose sunlight direction:


Examples of shots taken with cloudy conditions:



Examples of shots with correct sunlight direction + good
sunlight condition



Its always best to go for spots with correct sunlight direction
and try looking out for days with good sunlight conditions.
Conclusion: Got strong sunlight, no flash for ur
camera.