It also cannot do tasks it wasn't trained for. It can extend texts, read images and click on a desktop, but only because it's made for that.
The claim is furthermore that truly original thinking, the infamous leaps in understanding and creativity, happen by attaining points outside such a convex hull.
It's hard to rigorously verify or disprove this claim. Hopefully this helps build an intuition of why the claim is not as shallow and obviously wrong as it may seem initially.
But yes, metaphorically I think that's right.