Don't stress. If they are talking to you, then that is a good sign, and they flew you out -- so they must see something in you. You might want to review your code on Github, so that you can address questions, off the top of your head. I wouldn't change though. I highly suspect they just want to see if you know where you could have improved, etc. Rather than being some seasoned superstar who never makes mistakes. So a review on your part, then you can make comments about how you would change things now that you know more, etc.
Here is some general job search advice. Job hunting is more of a machine gun approach, where you try and shoot lots of things, rather than a sniper. I guess what I mean is, research and apply to 10 jobs, then you have a choice, and are not stressed if someone is being weird. Use excel or something, track your progress, write custom cover letters, do your research about the company, etc. When you don't have a job, job hunting is your job, so spend your time wisely and try and make good shots. You have the control. This will likely lead you to negotiate harder, appear to have more confidence, etc. In the long run, if you don't get it, there are tons of other opportunities out there. I once applied and was eventually hired for a public sector job, it took around 6 months to land it, tons of interviews, tests, phone calls, emails, security screening, etc. At the end, I just wanted the entire thing to be over with, one way or the other, so this phone call seems pretty minor, and I wouldn't stress too much.