The sound is re-constructed from the shaking of the leaves. It's quite analogous to the way the sound is initially constructed from the vibration of a speaker membrane. The difference being that the medium of vibration which is used to propagate the "sound" is digital video rather than air.
You observe leaves shaking when there is wind (a correlation). To test for causality you need to make an intervention. You still the leaves - the wind keeps going. You block the wind - the leaves stop shaking. There clearly is an asymmetry here. The physical equations may be symmetric, but this doesn't justify calling a microphone "speaker".
>The physical equations may be symmetric, but this doesn't justify calling a microphone "speaker".
Actually a speaker is just a microphone with very small adaptations depending on the use (polarity, noise sensitivity, etc).
But this is not about the wind, but about sound. The wind you describe is external ("You still the leaves - the wind keeps going"). But you can just as well have a wind produced by the leafs themselves.
One could say these objects are both. They pick up sound, acting as microphones, and send it back out by vibrating, acting as speakers (amplifying it by a factor of less than one). The camera acts as the microphone for ‘hearing’ that sound.
I think you could hear that produced sound with a traditional microphone, but you would probably call it the echo of the original sound, and it might be hard to hear it over the original, typically much louder, sound.
It would be much more accurate to say these objects are neither speakers nor microphones. It is not a surprise that all objects vibrate in response to sound waves. What characterizes speakers or microphones is that they are transducers converting between acoustic signals and electrical signals. None of these objects are transducers so it's not accurate to call them speakers or microphones. It is reasonable to refer to the system of camera plus software plus observed object a kind of microphone but certainly not to refer to the observed objects as speakers or microphones.
An aeroplane flies through the air and a submarine travels through the ocean. I can throw a rock into the air or into the ocean, that doesn't make a rock an aeroplane or a submarine.