Well, yeah. But it may be that, when talking to a co-worker about something, they point out some programming syntax you weren't aware of, just as a way of trying to be helpful. What's a good way to handle it?

You could thank them for pointing it out, say you're not sure you want to use it (if you don't think it's better) and then get the conversation back on track. And, hopefully they'll think you handled it smoothly and won't take off points, but you'll never know how important it is to them that you're fluent in Swift. Maybe not at all, it's just an aside?

Which is to say, usually you can't tell in an interview what they're really grading you on. It's nerve-racking, but you just have to try to seem reasonable and hope that works.