I'll have to watch that video when I have the time. I am no trained linguist, but this is a tricky business:
Are certain folk tale motifs widespread because they are really old?
Or were they so popular that they spread like wildfire along trade routes?
Or is it a matter of parallel evolution? For example, most human cultures have myths of "sleep paralysis demons" because "sleep paralysis" is a widespread human experience. And many cultures around the world have phenomena similar to the European Wild Hunt, because (I suspect) "the wind making odd noises at night" is also a widespread phenomenon.
I'd have to take a closer look at the science behind such studies to judge them.