Use TURBO mode to see the QR code. (Press the <Shift> key and click the Green Flag for TURBO mode). The "1 Line Challenge" is to produce an interesting pattern using only ONE line of code to calculate the color of each pixel.
This entry for the "1 Line Challenge" displays a QR code for the Scratch website. While it is theoretically possible to generate any QR code, it would require a lot of join blocks in place of the long binary string. . .