Actually, not at all. She said she's never seen it, not that it's impossible.
Where did she say "I've seen someone eat only fruit and they did not get fat"?
Actually, you can isolate "single food items" as contributing to obesity. Sugar and trans fats contribute to obesity, cauliflower does not. No one food item CAUSES obesity on its own, sure.
Also, where exactly did she say that fruit cannot contribute to obesity? She said she's never seen a case where eating fruit caused obesity.
Learn to read brah.