A submerged armour belt was not intentional torpedo protection

Did an armour belt ending up below the waterline create an early form of torpedo defence?

Only incidentally and imperfectly; the belt might resist some underwater damage, but its submerged position reflected a serious protection problem shared by several navies.

The question jokes that General-Admiral's submerged belt accidentally became an early anti-torpedo system. Armour below the surface might resist some underwater damage, so the idea is not entirely absurd as a description of the physical effect. It was not, however, a purpose-designed torpedo-defence system. The belt had settled away from the waterline it was meant to protect because the ship displaced more than intended. British armoured cruisers suffered the same dangerous consequence, so the example concerns weight growth and stability rather than accidental innovation.