My personal model of motion sickness is that either your inner ear is saying, "Hey we are moving" and your eyes are saying "No we're not!" (classic sea sickness/car thing). Or your eyes are saying, "Hey we're moving!" and your inner ear is saying, "No we're not!" (classic VR motion sickness).

So it makes sense with that model that you'd get motion sickness reading in the car. Your eyes are so focused on the fixed page you're not getting the movement cues you would if you looked out the window. The dots give you that cue somewhat subliminally.

I have a theory it could be slightly nauseating for one to try and read when not in motion while dots moved around the page like that.