That's not true, man. Don't forget, he TAUGHT people the means to focus chakra. The Uchiha and Senju ancestors are really just that.EVERYONE in the manga is directly descended from the So6P. EVERYONE. Everyone is either from the elder son of the S06P (uchiha), or from the younger son (Senju).
So like I said, it makes about as much sense to just 'appear' in Nagato, as it does Naruto, because BOTH are senju. I assume some things because of the evidence we've been given by Kishi.
Is Tobi a liar? Not necessarily. He DID lie about being Madara Uchiha, but for a very good reason. Would he lie about giving Nagato the Rinnegan? Sure.
However, we have this panel of chapter 559 that gives Tobi's story credibility:
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'It would appear that little brat Nagato managed to grow' - Madara Uchiha, right after he is summoned by Edo Tensei.
Then he says:
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This is HIS doing, meaning he knows who resurrected him with Edo Tensei. Then on the same page, Kabuto says he is HIS assistant, meaning he is the assistant of the person Madara is thinking of, which is Orochimaru.
Not only did Madara live after his fight with Hashirama, but somehow he lived long enough to encounter Nagato AND Orochimaru.
At this point yes, it's a fact that Tobi 'gave' Nagato the Rinnegan, all we need now is the explanation of how.
And I don't get why people believe, if Nagato WAS given the rinnegan, that it was by Tobi. Madara KNEW him, so he was alive during that time. I'm pretty sure we can say that Madara would be the one to have given it to him. And, as I said before, he called Tobi "that someone", so he probably doesn't know his identity either.
Tobi's EMS is the same as Madara's, so if Nagato has Madara's Rinnegan, there's definitely a technique we aren't aware of yet.
And I thought it was Orochimaru for a while, too. The facts did all fit, up until I remembered he tried to steal Itachi's Sharingan, which was long after Kurama's attack. So unless he switched his eyes back out for Madara's before this, I doubt it's him anymore. I'm starting to fall back into the possibility of it being Izuna, cause it began making some sense again.