X is Y used in Z. Does that mean X is not Y when it is not used in Z? A knife is a sharp object used to cut meat. How do I call the thing to cut fish?

Yes, I see how you can parse the definition your way, I didn't thought about that before introducing it.

> since it is an ADT, not anything object oriented

Yes, they have large overlap. To my understanding, the difference is, that OOP has inheritance and an ADT can be provided by the big god object. The latter I would refrain to call OOP, although it can be argued it still is.

I think our real discussion here is, whether a function entry that doesn't take an argument of the object type precludes it being a vtable. To me it is as long as this function is supposed to be a method of a single object and not for all objects in general, i.e. a global function.