The above graph analyzes the case. And as we can see, we have reference objects, trees and houses, most probably. The point is, with respect to the static reference objects, the airplane was projected to the same observation point. The reason it looked rotating is the view angle is changing. We know from our daily life, the perpendicular angular speed of view is indeed comparable with that of slowly moving bus. Both take seconds to make a sensible change. That explains why this can happen.