Just looking deeper myself - the 3 openings on the housing not described in this teardown are Venting ... and inside the neck is a metal collar that has been insert molded into the shell with the mesh over openings on both sides.
I was surprised at the hidden mic, and the sound channel they provided (seen on the frame to one side of the mic). The gasket between the bottom shell and PCA frame was clearly there to provide isolation and reduce the chamber size (you can see the gasket and it's mic direction in Step 12).
The one I am looking at now has kapton tape over the whole PCB with the little spacers on it over the button domes. Most likely to prevent the metal from on the button from shorting the PCB.