Go talk with some old people. You may be surprised. Occam's razor says skin flap. I've personally been around lots of old people (for non creepy reasons) and been startled a lot at what old age does to people, including this type of optical illusion. (Yes, I was looked at oddly by some people for staring at a bald dude in a suit/tie that looked very similar to this.)

Not trying to debunk mask theories, just saying there is more than one explanation for this specific instance.

Source: personal life experience. Others can corroborate if they've spent any amount of time around the elderly.