It's probably a reduced or dehydrated stock, made from the body meat and cracked shells, that is then strained and drained.
I make my own shrimp stock this way. When I have peel and eat shrimp, I save the shells and tails and simmer in water to make a shrimp stock. The flavor in the shells and in the little bit of inaccessible shrimp meat in the tail flavors the stock nicely.
It's probably too high carb, but I used to use this stock water in making tomato soup from a can. Then I'd add some shrimp (peeled) at the very end,
to make a shrimp bisque.
I was just watching a show yesterday on pollock fishing, and they showed the making of surimi (the fake crabs, lobster...). It was very interesting. It's actually made on the boats that catch the fish. Surimi is made from a cod-like fish called a pollock, but it can be combined with natural or artificial flavorings to imitate more expensive fish and shellfish like crab, shrimp. lobster... All the fish is processed and frozen the day it is caught, right on the boat. Fish fillets, fish roe (actually air-lifted off the boat to be taken directly to market), fish meal for animal foods and natural garden fertilizer.
If you check the different brands, the different imitation crab, lobster... have very different ingredients and carb contents. From very natural to very scary.