S-boats were not German torpedo boats

Did Germany send torpedo boats to the Black Sea, or were those vessels actually S-boats?

They were S-boats or motor torpedo boats; Germany's formal torpedo-boat classes were much larger, destroyer-like warships.

The German craft sent to the Black Sea were S-boats, which other navies would classify as motor torpedo boats. German vessels formally called torpedo boats, such as Type 1935 ships, were closer to small destroyers in size and role. A detailed Black Sea account would make the distinction explicit. For a broad comparison of opposing force strength, however, the terminology does not change the strategic balance being described.