Cooking & Baking

Usually it's meant in the original sense of sticky, glue-like…prime example being glutinous rice, which of course is gluten-free. "Gluten" itself is Latin for "glue" and evolved to mean any sticky substance; the grain-based protein was named as such because it's the glue that holds breads together.

So in your case, it meant a goopy substance made of fish, not a fish-derived protein!

ETA: Just to make things more confusing, in Asian cookery "mock" meats and seitan are pure gluten that's been processed and seasoned to serve as non-animal protein substitutes! So an unwary consumer could think they're avoiding gluten by passing on the Fish Gluten in favor of the Mock Duck…