You can't make anyone making source code public, only stopping them from distributing copies of code which you have authored. Copyright and patents works very differently, and its quite hard (impossible) to copy source code wholesale from a interview by accident.

If they did makes copies of an applicants copyrighted work and distribute it, then they could get sued. Some companies has been know to explicitly ask applicants to bring source code from previous work places (also called industry espionage), and those been clearly intended crimes and not something that just happened to company during the process of an interview.