I think he meant like combining those two (Uchiha and Senju) gets you the sages power, and when obito said nagato was the 3rd path he meant nagato had the power of Rikudo.
In the previous page, he clearly said thatObito was telling the story of the relation between Sage, Senju and Uchihas, but you only pulled out a piece of it.You must be registered for see images
Two clans =Senju and Uchiha
Two Bloodlines = Sharingan and Mokuton
Indeed. I think it was a mistranslated.