You're sort of not wrong, touchid uses a capacitive sensor vs. a visual/camera sensor which has become more common in other devices. What this means is in theor

You're sort of not wrong, touchid uses a capacitive sensor vs. a visual/camera sensor which has become more common in other devices. What this means is in theory you're measuring the electrical behavior of the outer layers of skin, and Apple claims goes as far as measuring subdermis. (This is also is why their touchid scanners don't work on wet fingers as the behavior is thrown off). However, they are showing their attack working on a Macbook Pro with touchid, which uses this sort of reader. So it's easier to fake in practice than it is in theory. Whatever material you lift the print off of should have to mimic the capacitive behavior of the finger and this looks like it busts Apple's claim that it can read the lower layers (or it tells us their default sensitivity is set too low for convenience)