GPIO is abbreviation for General Purpose Input Output. In addition to 5v, 3v and ground other pins allow for turning on/off to complete an electric circuit in response to logic running on the pi, or connect sensors, or control other devices with I2C, SPI and sometimes UART. The screen attached to the Argon is handled with SPI using drivers on the pi. The other case is connecting the screen using DSI interface which is separate from the GPIO pins