That big wood mixing bowl looks a whole lot like one we have in our baking museum, the only difference is that ours is a lot older. It served the same function though. The neat thing about wood mixing bowls and wood dough troughs (commonly used here in the U.S. until the 50's especially in cracker production) was that they would hold bacteria (lactic acid forming bacteria/lacotbacillis) and inoculate the dough that was placed into them much like we would use a sourdough starter today. When the cracker industry moved away from the wood troughs they had to identify the specific bacteria, culture it, and add it to the dough to get the same finished flavor profile that they had with the wood troughs.
As for mixing the dough without power, there is a pizzeria in the Pittsburgh area where the owner has a long stainless steel trough, he measures out his water in a pail, adds it to the trough, adds flour, salt and sugar, then wets his hands and arms and spreads cake yeast over them as one might use soap, he then proceeds to hand mix the dough just until it comes together, after that he allows biochemical fermentation to do the rest of the work for him. It is quite a store, people come in just to watch him make his dough.
Tom Lehmann/The Dough Doctor