With Cathode ray TVs only a single pixel at a time is on, it relies on our eyes having bad enough temporal resolution, if you have Superspeed eyes you will see just a coloured line/pixel moving on screen
That's not quite true. Only one pixel is being activated at a time but the phosphors continue to emit light for many pixels. In practice you get a handful of lines lit to varying degrees at at time. Maybe 1-2 lines quite brightly lit and then a trail of lines that are fading pretty significantly (but still emitting light). They yes, our persistence of vision fills in the rest to provide the appearance of a fully lit screen.
This video has some great slow-mo of CRTs https://www.youtube.com/watch?v=3BJU2drrtCM&t=160s