Gullible fool believes whatever he's told. How could anyone make such an assessment? From the very beginning we have known that COVID can be very mild, can be serious, can be fatal. That was before the vaccine. You survived COVID? That's nice. But you can't be sure the vaccine played any role in that at all. And some might suggest that the vaccine made you more susceptible.
He misunderstood - without the vax, he would have been fine and healthy. With it, he ended up deathly ill in hospital.