As a freelance back-end developer with various co-founding experience this question speaks to me. I think it's all a matter of perspective.

Looking at it from a development perspective the two can mean the same thing: we pivot and so we need to add new features.

However, in my experience the key is to look at pivoting from a non-development perspective. As mentioned in parent comments you pivot to find a product market fit. That entails finding your audience and the problem you're solving for them. Those questions do not require a product, but a human understanding. Questions like 'is it actually a problem they need solving, or a slight convenience?' and 'how are they solving their problem without my product?'.

By pivoting quickly in that space you don't get bogged down by technical issues or challenges that don't even matter, and the real solution might be a week's worth of time.

Pivoting means you are solving a new core problem. Adding features keeps the core problem intact.

Pivoting involves picking a different problem to solve. Or who to solve it for. Or rarely, a radically different way to solve it (usually involving starting anew). Features and other product work is tweaking on the solution side, assuming there is nothing wrong with the chosen problem.