This is an extremely poorly designed experiment that shows nothing relating to handedness.
The thumb on top depends strictly on how you lace your fingers...regardless of whether you are right-handed or left-handed, blue-eyed or whether you had corn flakes for breakfast.
Lace your fingers with the left little finger in the bottom position. Now your right thumb is on top.
Lace your fingers with the right little finger in the bottom position. Now your left thumb is on top.
This survey may measure gullibility but it certainly does not measure traits related to handedness. Either the poster is pulling our chain , the exercise is measuring gullibility or the science education in the education racket is even stupider that I think it is.
So then the experiment should actually focus on the pinky on the bottom! Regardless of the reasons for the top thumb, would be interesting to see how many right handers put the right pinky on the bottom or vice versa, and is it related to handedness at all.
Maybe its related to the religion.. As a Catholic attending Catholic education most of my life, I did a lot of hand clasping... Hmmm... Maybe it was Mrs Youngbloods fault that my right pinky is on the bottom! I demand reparations!