How are those statements contradictory? UI design is a separate discipline from software development just as automobile design is separate from automotive mecha

How are those statements contradictory? UI design is a separate discipline from software development just as automobile design is separate from automotive mechanical engineering. I am both a developer and designer. While it was never my sole full-time job, I've done a few thousand hours of front-end development in various environments both professionally and for FOSS projects. I'm quite familiar with how all of these pieces fit together and completely comfortable with my chosen professional path.