In this particular example, all it does is reverse the order of return type wrt arguments and function name. I still find this syntax more readable with complicated return types because you no longer have to carefully parse it to see where the type ends and the name begins.
In the more general case, having the return type follow the function name means that it can reference parameters in sizeof(), decltype() etc.
I can't speak for the C++ example, but in your code snippet `->` points to the return type. The function takes an integer argument and effectively turns it into a tuple, so: `f(i32) -> (i32, bool)`.
auto SmallestFactor(int32_t n) -> std::pair<int32_t, bool> { ... }