Well, knowing very little about taegu, never actually having tried it, and even less about Korean, never having spoke it. I would assume that taegu refers to the condiment, not the particular fish. That is, it can be made with fish besides cod. For example, take ketchup- most people are only familiar with the most popular tomato variety but there is also walnut ketchup, mango ketchup, ketjap manis, etc. Chances are he simply had sea squirt taegu… here is a reference to Cuttlefish taegu.
Nori Linguine Salad
8-ounce package linguine
1-pound package imitation crab, chopped
3 ounces taegu (Korean seasoned cuttlefish), chopped
1/2 bottle Tropic Oriental dressing
1/2 bottle furikake (seasoned dried-seaweed condiment)
Boil linguine about 10 minutes and rinse. Toss together all ingredients. Chill.