It was Vivio's vision. "What would happen if I got hit with that attack?" and that was the likely result. It's a common thing in mangas like this, another example is in Negima when Koutaro envisioned what would happen if he tried to attack Fate while cloaked. Didn't turn out too well for Koutaro so he didn't act.
Though if anything one should compliment Vivio on being able to sense Shante's, for a lack of a better term, 'killing intent' and being able to tell what sort of attack was coming.
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