They compare it because the mangas are one in the same. Itachi just discovered that not is he part hollow and shinigami, but that he is also part quincy. A butterfly effect than occurs in which Itachi finds out that he is also part Uchiha due to his nonchalant, carefree attitude and will take revenge for the ones he loves; part senju where he finds out he has a massive amount of energy stored up within him at anytime; part super saiyan where he can powerup from normal mode to bankai mode, bankai mode to quincy mode, quincy mode to hollow mode, hollow mode to super bankai mode, super bankai mode to super saiyan 14.
It all relates to each other.