std::minus vs abs

[kobi-ca]

https://github.com/codereport/Talks/blob/741a79cc95ccfe14b5951483d563267253793065/2019-05-CppNow/AlgorithmIntuition/Slide-139.cpp#L7

You changed abs to std::minus since in abs(a-b), we know b >= a.
So how changing it from abs to minus works?
wouldn't this generate negative number?

Thanks,
Kobi