[grishka]

Thinking about it a bit more, no, your argument about touchscreens doesn't make sense. The terminal OP looked at runs Linux on the "insecure" side, but the keypad is still passed through to that the same way the touchscreen would be passed through to the Android SoC, because it's used to navigate menus and enter the purchase amount. The Linux side would still send some sort of command to the CPU core that runs the "secure" OS to initiate PIN entry, and it could still just do what you describe.