When I make pizza dough, I usually make a batch big enough for 4 pizzas. Then I individually portion out the dough and stick it in the freezer so it's ready for quick weeknight dinners.
This is what happens when you forget to open up the baggies before letting the dough thaw and rise. The "air" that filled up the bag is carbon dioxide that is made when the yeast starts to eat up the sugars in the dough.
This dough is Whole Wheat Pizza Dough from Eating Well.