[Someone]

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.

[mattnewport]

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.