I think what they meant is something along the lines of:

- In Math, there's often more than one logically distinct way of proving a theorem, and definitely many ways of writing the same proof, though the second applies more to handwritten/text proofs than say a proof in Lean.

- In programming, there's often multiple algorithms to solve a problem correctly (in the mathematical sense, optimality aside), and for the same algorithm there are many ways to implement it.

LLMs however are not performing any logical pass on their output, so they have no way of constraining correctness while being able to produce different outputs for the same question.