[Retric]

The direction of propagation is the way sound and light point to something. It’s why people listen to music in stereo rather than mono which sounds weird and also why telescopes work. Again simplified, but when you hear a sound with your right ear before the left that tells you something.

> arrives after the (slow) plane

That has nothing to do with the article, just your misunderstanding of what was described. At every instant in time the sound you hear corresponds to something produced by the aircraft at a specific moment in the past. Thus when someone is listing right now they hear a specific sound not the aircraft taking off.

Light from an aircraft also takes time to arrive. It might not seem relevant because of the speeds and distances involved, but the exact same thing is happening and it is relevant for light in other contexts.