It's called "uniform function call syntax" because it comes from D unifies function calling between member functions and free functions. It's not called "uniform function declaration syntax" because the declarations are obviously not unified. The fact that you have to declare functions shouldn't be relevant to the name.

And of course rust people found a way to make this all about rust. I highly doubt the Clang devs are thinking "hmm we're really close to compiling rust but we just can't figure out UFCS." And C++ is not at all a sinking island.