Orange peel is an effect that looks just like that of an orange peel. Not only does it happen when airbrushing but it also occurs when you use rattle cans as well.
Orange peel effect can be corrected post painting by simply wet sanding the paint to rub out the effect. Car builders do it even on 1:1 scale projects.
Its partially caused by paint not self leveling and drying at different rates.
When you wet sand you knock down the high spots and level the paint surface to a more even consistency.