The biggest difference between UX and UI Design is that UX is about the goal, and the UI is about how you get there. UX and UI Design always overlap.
The UX Designer’s job is to start with the psychology of the user. UX Designer’s must remember that the goal of the product is to solve a person’s problem.
UI visualizes that path, making it easy for people to follow. It’s common for companies to want the designer to do both UX and UI, because of how closely the two are linked