At the interview stage, the candidate has been looking at your use case for at most a couple of hours with very little context. Assuming you've done any work on

At the interview stage, the candidate has been looking at your use case for at most a couple of hours with very little context. Assuming you've done any work on X and that you are competent, X is probably a good choice or at least there's good reason to believe it is a good choice. It might be nice if the candidate asks why you chose X over Y, but they shouldn't seriously propose that you should switch over to Y. Best case scenario they're assuming their little glimpse gives them a deeper understanding of the problem than you, which suggests they're cocky, worst case they may be deliberately selling you on a potentially worse solution that they just happen to be more comfortable with, ie they're inflexible. A good developer should wait until they know what they are talking about before they form an opinion on what would be the right tool for the job.