Um...the fuck are you on? It's the same fucking attack. Both Hiruzen and Tobirama were talking about the black shit that Obito was using both before and after he gained control of the Juubi. Hiruzen didn't state it as fact. In fact, he was referring to how the shape could be altered as why it was above Jinton. Tobirama, after seeing that Minato was regenerating after getting hit by it, deduced it was probably a Yin-Yang based attack designed to nullify jutsu (not a 7 element combination).