baron 1 shot bug

I had over 1500 hp on a tanky braum, and team headed to baron. As soon as I stepped in baron to auto attack......BOOM HEADSHOT, NOSCOPE 420 kappa kappa. I had guardian angel buff up and I died to 150 magic damage from baron. I was the only one that died. GA buff did not activate. Is this a bug or did someone hack baron?