I think it's just that calling it "maths" tends to give a false sense of certainty where none is warranted.

Example: All the really clever math you use to make an encryption algorithm is all 100% correct. Then all the really clever math you use to show that it would take the heat death of the universe to crack your clever encryption is 100% correct. The user uses 'password' as the key; How does your crypto stand up to a brute force? Is that your algorithms fault? Did your difficulty proof lie to you?

I know key length is a well understood. In terms of how algorithmically "valid" real world data that can otherwise torpedo entire complex systems, it's as good an example as any.