I applied for a Web developer job in Quebec City and they call me back for a phone interview everything went well it last for over a hours and at the end they ask me to send code simple and a portfolio but in my research about the company and their products I found a PHP error(bug) in their app. Should I tell them or I will look like a total jerk and blew my chance for a interview? I know it might sound stupid, as a Jr developer I did 2 interviews they didn't went so well and I am very interested in this position part of my question is like a big lack of confidence so to make it short should I tell them about where is the error and how to fix it?

Thanks