It isn't really debunked. But this method of saying which side is "dominant" is. Each eye's information is sent to the opposite hemisphere (edit: as well as the corresponding hemisphere), so the idea is that if you see it moving left, your right hemisphere is processing the information first, then your left hemisphere.

But there is absolutely no conclusive evidence to suggest this is true, and to show these kinds of things on The Daily Telegraph is a pretty big disservice to teaching people about neuroscience, I think.

This doesn't mean there aren't differences in the hemispheres, but just that visual tricks like this are probably not accurate at all for determining hemisphere dominance (if such a thing exists).