I would say that it is the term "UX" that is the confusing part of "UX/UI".

By Don Norman's original definition [0], it is not merely another term for "UI" but specifically when you do have a wider scope and not working with a user interface specifically.

So, the term "UX/UI" would refer to being able to both work with the wider scope, and to go deeper to work with user interface design.

0: https://www.youtube.com/watch?v=9BdtGjoIN4E&t=10s