What Kishi has used there is an overlay technique and let me tell you , he uses it a lot in the manga. Lol For a normal reader, the conclusion would be "Sarada mentioned Sasuke's name and Sasuke gave an involuntarily reaction because of the chain of fate".
While that thinking is logical, Sasuke's actions don't make sense via that luck logic.
Namely this,
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Why would Sasuke pull out his sword ? He would only do that if he sensed a presence which could be a potential threat. So, Sasuke pulling out his sword shows someone (Spiral Zetsu, Orochimaru) following Sasuke with evil intentions in mind.
Kishi might have left that panel as a teaser for a part 3.
One theory to explain that was that Hashirama's powers originated from the Shinju and Black Zetsu might have had a hand in implanting Hashirama with a seed of the Shinju (Giving him wood release) to ensure future compatibility of the Rinnegan with Madara. This theory was made by me and Veritas.