I think they mean atom as in, the smallest unit that everything is built out of, not the scientific atom. I.e. not a single polygon is placed by a human artist and the sets aren't pre-designed with just some random variation.
But looking at the demo that doesn't seem to be true either.
Eh, I think the more charitable reading is they meant a physical atom, but in the sense "not a single atom has been designed by hand."
It's like if you made some algorithmic music and claimed every nanosecond was generated automatically, even though we tend to think in terms of notes that are orders of magnitude larger.
If they really expect anyone in the gaming community to believe they're rendering each blade of grass with a few Octillion points or polygons, they're absolutely insane.
But looking at the demo that doesn't seem to be true either.