I once as a kid saw a shadow of the grim reaper swipe his scythe at my PE coach... a few years later he died of cancer. I feel like I coulda told him to see a doctor and get checked up and they might of caught it early. But that would of required an adult to take into account the word of a 3rd grader.
You mostlikely didn't realise what it meant at the time. Nor can you alter someones fate. I wouldn't think too much about it, nor blame yourself.
Legion.