Well to add, it's technically unknown for sure if food causes a flare up, but science has enough information that Crohn's itself is not caused by "food" per se, but a microbe or bacterium in food, or a virus, etc...that is IN the food, might. Food can make a flare (or even a normal person) worse off, though, but that's individualized.
As for causing flares, food may or may not, it's unknown, and probably individual too, as in where your Crohn's is, and what kind of foods do what to you. More questions and mysteries instead of answers, I'm afraid.