Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
My guess is she's proving that the yolk doesn't break easily.
It's a neat looking method but a lot of fooling around for what can so easily be done by cracking the egg in 2 and pouring the yolk back and forth in the 2 halves a couple times, I've done thousands of eggs that way when working in our family's restaurants over the years.
I'd like to separate 5 or 6 eggs using that method to see if you can do it multiple times easily as I only eat the whites in most cases. I'll try it on Sunday's omelet!