Are you confusing the implementation of these operator overloads with their signature? The spaceship returns {neg, 0, pos} and that's why the implementations are like that.
The values of these comparison categories can be compared against the literal 0 (not any int, not an int whose value is 0... just the literal) using any of the six comparison operators...
IIUC it's referring to how you can safely evaluate the return value from a spaceship: by comparing against literal zero. (not how you would overload a comparison with literal zero).
