I mean it's a fact Fury under prepared for him. He'd literally signed beforehand to fight Usyk 2 months later and so clearly thought this would just be a cake walk.
IMO it's more that Francis actually has a chin and so could walk through Fury's shots to land his own. Fury and his team I guess hadn't really noticed that aspect of his game and so weren't prepared when Ngannou wasn't going down from the shots Fury landed and therefore actually making it into a fight. Francis Rocky'd Fury.
Ngannou will have succcess against any of the boxers who are relying on greater technique to beat him as he's got an iron chin and nuclear hands. Some will do better at outpointing him, but he'll probably always be able to cause problems against those guys. Nobody goes through a fight completely unscathed except in a quick KO.
That's why the Wilder fight's the most interesting as Wilder's crumpled everybody he's ever fought and every chin breaks eventually. Walking through what Wilder's throwing his way is a whole nother ball game.