Yes, "off the coast" means in the sea, close to the land.
According to the provided reference, "off the coast" signifies being in the sea close to the land. For example, "The accident happened three miles off the coast" means the accident occurred in the sea, three miles away from the land. Similarly, "It's a tiny island off the coast of western Ireland" indicates the island is located in the sea near the coast of western Ireland.
