Need info/tip

I want to know what really happened. This is in 6.2.5. I used an SP3 when Corvus was at 1% health and expected him to be KOed. But he did not and my champ got KOed. Can someone explain this?
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Comments
"Do not go gentle"
When they have one or more of those coloured charges, any effect that would kill them is, I believe, negated. And the attacker takes damage based on their attack.
I dunno, read the node anyway