That's actually quite a controversial statement that many professional mathematicians might beg to differ with.
Viewing mathematical results and axioms as being totally invented, opens the possibility of being able to just will contradictory proofs into existence, and that is simply not the case in practice. Mathematics might be more for description than definition, but what it's describing isn't usually the physical world, it's the logical limitations of certain principles. And if these principles are found to be reflected in some aspect of the "real world", then the corresponding mathematics becomes applicable. But you can't just pick any arbitrary axioms/principles and have them automatically be mathematically coherent either, so again we're limited in the maths that we can "invent".