On reflection, the saying at the top of this post is not true. The implicit assumption that fails is that the only thing one can say about all the apples in the world are things that are true of all those apples. But there are many other things one can say about all of the apples in the world. One can, for example, talk about the distribution of apple sizes, similar to the way one could talk about the size of a particular apple. For any feature of an apple we can talk about the distribution of that feature among all the apples of the world.
On reflection, the saying at the top of this post is not true. The implicit assumption that fails is that the only thing one can say about all the apples in the world are things that are true of all those apples. But there are many other things one can say about all of the apples in the world. One can, for example, talk about the distribution of apple sizes, similar to the way one could talk about the size of a particular apple. For any feature of an apple we can talk about the distribution of that feature among all the apples of the world.