Anyone can be paid less for the same exact position, especially in salaried management type positions. I have seen that many times. It's called negotiating skills and the willingness to walk if you don't get what you want.
Sure. The paper, that was cited in the article you referenced in the OP, referenced another paper that showed that negotiators statistically negotiate harder with women than with men. I didn't go down further in this rabbit hole because it's not worth my time - but if you care enough about the issue, you could look that paper up and comment on it.