[korantu]

Suppose observer just woke up / heard plane that is passing overhead.

Very reasonable assumption, as the plane might have taken off thousands of miles away, and will land thousands of miles away in the other direction.

In this case, no point talking about takeoff sound, as it is not detectable already at these distances.

Humans can detect reasonably well which direction the sound comes from. This direction will not match the direction they observe the airplane at.

The article is describing the mismatch between plane real position and the plane position we would detect if we were just listening to it.