I think that’s getting too literal. You press a thing, it does something. Functionally it’s a button regardless of what it looks like.
When I say metaphor, I’m talking about referring to something that isn’t functionally a button but might be described as such. Candy buttons, a belly button (outies, anyway), a nipple, or anything else that might also be referred to as a nub.
Huh. The buttons on my PS3 require no force; they’re capacitive sensors and I can lightly brush them. The power button on my Xbox 360 is a physical button. I clicks.