Chrome 51.0.2679.0 
OSX 10.11.4

What steps will reproduce the problem?
(1) Visit https://permission.site
(2) Click on audio and grant.
(3)

What is the expected output?
If there is a page action, it shows a microphone.

What do you see instead?
It shows a camera.

I think it's okay for a camera icon to subsume the mic if both camera and mic are active, but showing a camera for audio-only is surprising ("wait, I thought I only granted my microphone!"). You shouldn't need to click on the icon to figure out what it means.

I presume that this is not a conscious design choice, but rather an artifact of the historical combined content setting for both media (mic and camera).