Why HMS Warrior was called an ironclad frigate

Was HMS Warrior a frigate or a ship of the line?

She was technically an ironclad frigate because of her single gun-deck form and cruising role, even though her power places her close to the line-of-battle tradition.

Warrior does not feel like a small frigate when judged by size or fighting power. Her technical classification followed the single gun-deck form and the expectation that she could cruise independently. Ironclad frigates and ships of the line soon converged into a broader battleship lineage. A familiar modern size hierarchy therefore fits nineteenth-century terminology poorly.