Job searching in small community

Ok you guys I want to ask for your expertise. I live in a small community (nursing is a small community too), and I have recently interviewed for a job, where the nursing manager also knows very well, my current boss. Also the new nurse manager helped start the company I currently work for. I put in my application that I would not like my current boss to know I am currently searching for a new job. I have some suspicions that she may know. Are there any laws that protect us from that?
Do you know how your current boss found out? Can you prove that confidential information was leaked? Or could this information have been casually transmitted?