Here's a relevant quote:
Now some quotes from the yet unreleased Azeroth's warning scenario: (https://www.youtube.com/watch?v=8xNMUjkHllk)When Azeroth's spirit speaks ta me, it's like a song. There's beauty in it, even when her message ain't exactly clear.
Definitely doesn't sound like a "song". Why would Magni feel pain if it was really Azeroth talking to him? Now some more quotes:Let her thoughts flow into... aaaaghhh! Sands soaked in pain. Rivers. Rivers of blood. Skies of flame! A sword... in the darkness. The wound is burning! Sargeras...
Garrosh:Wrathion:I have seen it! I have seen mountains of skulls and rivers of blood, and I will have my world!Seeing a pattern yet? We know for sure that it was Y'shaarj who showed Garrosh visions of rivers of blood. With Wrathion we don't know yet, but it's likely that he saw visions either because N'Zoth invaded his mind like he did with all other black dragons, or because being purified by that titan device in Badlands gave him some sort of a connection to Azeroth. It seems very unlikely that Azeroth would show Magni something as demoralizing and pointlessly brutal as rivers of blood.Wrathion: ...Great Crane. You have not seen what I have seen. ...the fire that once burned the sky will return. It is inevitable. The Burning Legion WILL find Azeroth. Seas of blood, cities in ruins! Who are we - one divided world - to stand against a legion? You speak of hope. Believe me, the thinnest silver of belief that we might somehow survive the coming devastation is all that sustains me.
tl;dr: N'Zoth is weaving in his own whispers with Azeroth's visions to confuse Magni. Azeroth shows Magni stuff that legitimately concerns her (Sargeras), while N'Zoth is trying to break Magni's will.