"They have the concept of "minus", which is just another way of adding with a negative."
You have chosen to generalize it into the anstract concept of negative numbers. That doesn't mean that negative numbers are a fundamental truth about nature to be discovered.
Think about it like functional programming. Is that discovering some natural law of computing? Or is it inventing a new way to express computation? Of course it must be the latter, because you can compute anything without the use of functions.
Inverses are just an abstraction that helps you rearrange operations.
You'd think something like accounting would need negative numbers, but nope, it gets along just fine without them.