I think the idea is not that the design is without a grid, but more on how it handles being resized. The video in the article does a good job of explaining it.
1fr 1fr 1fr 1fr ... 12times or so
Many CSS frameworks will provide a default grid system like this, and many designers will think in terms of such a grid.
But the author suggests that this is too rigid. And in fact a frontend developer will then have to interpret the rigid grid to be more adaptable and have either multiple flex grids for different breakpoints or use CSS grid to express more flexible flows.