Let's start with the meaning of User Experience.
Summary: "User experience" encompasses all aspects of the end-user's interaction with the company, its services, and its products.
Source: NNGroup https://www.nngroup.com/articles/definition-user-experience/
You're not only responsible for a logic design. UX is the center of many aspects which will influence the user's experience on the website / system, including interaction design, motion design, visual design, loading speeds, photography, etc. and the implementation of your work. When you're able to talk the language of the developers you're working with, it will speed up the process and it will help you to understand the possibilities and restrictions.
What Google says
We’re looking for our next Noogler - someone who’s good for the role, good for Google and good at lots of things.
Things move quickly around here. At Internet speed. That means we have to be nimble, both in how we work and how we hire. We look for people who are great at lots of things, love big challenges and welcome big changes. We can’t have too many specialists in just one particular area. We’re looking for people who are good for Google—and not just for right now, but for the long term.
In our discipline, new trends and discoveries are made each month (if not every week). For example, motion design has become a big part of the user experience in apps, so it helps if you know the basics of motion design in order to find the right people and communicate your needs.
Startups and small companies don't always have the budget to hire a UX Designer, a Front End developer, a Visual Designer and more related specialists. They are looking for a superman who can do it all by him self.
Do you need to learn new things? Yes. It doesn't hurt. Things change quickly in this discipline. You don't have to be a specialist in Front End Development. But if you have basic knowledge, you will be more flexible.