The term "Pétillant Naturel" refers to the production method. This is not new, but as "méthode ancestral", so well-known method of sparkling wine production known for centuries. Without the addition of yeast, sugar, must or otherwise, the pearly natural wine may ferment in one go. During this fermentation, it is filled into the bottle.
The last stage takes place under closure (bottle cap). This keeps the resulting carbon dioxide fresh. And because of the natural yeast found on the skin of the grapes and needed for fermentation in the bottle, Pet Nat is slightly cloudy.