Not to argue with the BBC, but this statement is just factually incorrect. Desert sand is not suitable for concrete because it is poorly graded and is all essentially the same size. Concrete mixes call for sands of various grain sizes, and so to use desert sand you would need to mix in these other sizes of sand.

I have seen this rumor repeated often and I think it is journalists trying to explain something they don't understand in a way that seems intuitive.