New employer offered my expected salary - but with Employer KS included - push back?

I just received a job offer that I'm very excited about. However, during the interview I stated my expected salary to be $X, which they have met in their job offer with one caveat:

The employer KS contributions are included in the salary.

Perhaps I've been fortunate to never encounter this scenario before, and now that I've researched it more it looks to be a pretty common practice- it's called a salary sacrifice. So when the HR lady explained this to me I was a bit amused in her wording, saying that "it's a great perk if you're not a KS contributor as you will take home more money." Well, like most people I am a KS contributor so no it's not a great perk.

Since I've never encountered this before, I feel like pushing back to get it renegotiated as my expected salary was exclusive of employer kiwisaver contributions.

I'm just wondering if this is reasonable to do or is it my mistake for not being clear in the interview?