Pretty sure everyone else understood the meaning behind the sentence ‘you can get protein from lettuce and apples’. You need a certain amount of daily protein intake for a healthy diet and the comment implied you can get those from lettuce and apples. It is technically kinda true if you take it literally, but eating 5kg of lettuce is not practical.
That was the point and I think you know it.
Play this argument in your head: ‘You need calories to survive’ - ‘You can get calories from concrete and sand’
In that situation, would you seriously argue that those actually contain nutrients at 0.0001 kcal per 100g? This was not very far from that.