Yes, I believe I have heard that said before, if not in exactly those words. And while I do not dispute this to be a valid point of view, I don't find it to be the only valid one. One might say there is difference, even if that difference is within the one, and even if the difference owes its existence to the dream. While the dreamer dreams, there is difference between the ten thousand things in the dream.

The problem with talking or thinking about oneness, is that one creates with the dialogue or thought, the concept of not oneness. Perhaps, there is no other way to discuss it and the only solution, if there is one, is not to discuss or think about it at all, and then only the one mystery remains.

Tao Te Ching - Lao Tzu - chapter 1

The Tao that can be told is not the eternal Tao.
The name that can be named is not the eternal name.
The nameless is the beginning of heaven and earth.
The named is the mother of ten thousand things.
Ever desireless, one can see the mystery.
Ever desiring, one can see the manifestations.
These two spring from the same source but differ in name;
this appears as darkness.
Darkness within darkness.
The gate to all mystery.