I'm not quite sure what you're saying here. My assertion is that a visible image persists on the screen longer than it appears in the slo-mo clip. You can just point a camera with an adjustable shutter speed at a CRT and see it for yourself. Here's an example (might need to copy the URL and open in a new tab, they don't like hotlinking):

https://i.sstatic.net/5K61i.png

The brightly-lit band is the part of the frame scanned by the beam while the shutter was open. The part above is the afterimage, which, while not as bright, is definitely there.