Smart pointers do not necessarily use reference counting. std::shared_ptr is reference counted, but std::unique_ptr is not. Needless to say that std::unique_ptr should always be the default choice and std::shared_ptr only used when actually needed.
I think you’re making a joke, but reference counting is different than what a unique pointer does. (a destructor is not the same thing as a reference count, even if that reference count is limited as you suggest.)
No, I don't think it's a joke. It's just that when your counter is limited to values of 0 and 1 only, you can optimize it so heavily it almost looks like a different thing entirely: binary semaphores are usually called mutexes, but they're still semaphores.
like the other comment said, std::unique_ptr is not ref counted. Ref counting is one of the ways to implement garbage collection but it is not garbage collection by itself. C++ does not have garbage collection.
C++ does not have garbage collection in the standard library, just as shared_ptr was not part of the standard library in the past. You can currently have optional garbage collection in C++: https://github.com/pebal/sgcl
