This seems to be a swipe at meditation, which empties the mind of thought. If you tell yourself to think of nothing, you will eventually thing of all sorts of things. My psychologist told me to try this while meditating and it really works. When extraneous thoughts come through, just acknowledge them and let them pass along. Don’t dwell on them.
My own way of meditating is to close my sees and focus on the end of my nose and focus on my breathing. That allows me to meditate fairly well.
But to try to think about nothing will not work. You will have more thought than you can shake a stick at.