everything is. whitespace is an important part of graphic design, especially margins. think about text that's too close to the edge is the page or screen.
i was speaking generally, which is why I mentioned pages as well as screens. that's more of a web design distinction; never really heard of padding in any other context.
but if you were to have a qr code on your website, you're right, making it padding would make more sense since the border, real or imaginary, would be outside the quiet zone because it's technically part of the code.
I think that was the point of "someone rescue me from frontend dev" - if they're doing so much frontend design work that they instinctively get pedantic about padding vs. margin, they need help.