Why isn't `std::unique_lock::owns_lock` called `owns_mutex`? [on hold]

Mutexes and scoped locks should not be confused, but somehow std::unique_lock::owns_lock "tests whether the lock owns its associated mutex" (quoting cppreference.com).

A lock on a mutex owning a lock doesn't make sense. Why hasn't the standard called this owns_mutex or is_locked?