Then, the said UX designer is not a true UX designer.
User experience involves stuffs other than visual appearances. They must also take care of interaction, information architecture, usability. Decreased usability is a symptom of failure of misdesign.
People learn about these topics at different period of their life.
The most important thing, to me at least, is to work with people open to learning and exploring something new. People who, when realizing they lack of a certain competence, goes curious about the topic rather than denying it.
A good UX designer might not know these topics before they are hired, but they will be happy to explore when they heard of the terms.
User experience involves stuffs other than visual appearances. They must also take care of interaction, information architecture, usability. Decreased usability is a symptom of failure of misdesign.