When I vacuum seal chicken pieces, freeze them, and then thaw them again, there is always a small amount of liquid in the bag after the thaw. When this liquid hits hot oil, it forms a crispy, airy puff that is absolutely delicious. I'm trying to figure out what the liquid is, and how I can extract more of it, so that I can make crispy fried chicken liquid for garnishes.
When you freeze meat the water in the cells crystallizes into ice, and in some case ruptures the cell walls. When you thaw the chicken again, the contents of the ruptured cells' are free. These are mostly the water, and the cells proteins.
Additionally, processed meats often have some water and additives added to the at the factory.
The "juice" you are seeing is probably a combination of these things.