Why is boiling water used?

Thanks. It makes sense now. I don't have much experience with dough. I make my own bread and pizza dough but haven't ventured much further than that. Bakers are scientists. Thanks again for the info. Wasn't expecting it to be so informative.

Aha, not totally wrong. There's a bit about the explanation of hot water dough: http://www.seriouseats.com/2011/04/the-food-lab-how-to-make-scallion-pancakes-chinese-appetizers.html

As an Asian who's made countless batches of hot water dough, I've never thought to question the reason behind the hot water, but I suspect hot water makes the dough more malleable and easier to knead than a dough that was made using cold water, which are often tight from overworked gluten and require long rest periods. Hot water relaxes the proteins and shortens rest time. I also think the hot water also half-cooks the flour, thus speeding up dumpling cooking time.
I could totally be wrong about the science behind it, but I think there's a marked difference between dough that's been made with hot water and dough kneaded with cold water.

I make Potstickers all the time and don't know of the recipe from Molly. After you brown the potstickers on one side you need to add water or broth to steam them to cook them through.