Eh, kind of. If you're rendering, for example, a Table with a lot of TableRows and change one of the values in the data array being passed to Table.props, you'd return true from Table.shouldComponentUpdate, and then each child TableRow would need to run its shouldComponentUpdate, even though only a single one really needs to update. So the argument is GP is making is that it's more efficient to directly update that single DOM element rather than update the data and then perform the calculations to determine that we need to update that single DOM element.
True in theory, but as long as each TableRow implements the PureRenderMixin and the Table render itself is efficient, you're going to need a lot more than a thousand rows before React has any trouble hitting 60fps in my experience.
But if you can't meet both those conditions, that sort of thing definitely can get quite slow.
