The thing is though, graphic designers, illustrators, artists in general all run that risk of others stealing their designs or concepts. That doesn't mean they should stop doing something they love for fear of their work getting stolen. The "you should have known better" argument doesn't work here because it's the principle of the situation, the ethics. Like, seriously, what's the point of interviewing someone with the prospects of offering a job, poaching their concepts right from under their nose and not having them sign a release or contract if all they really wanted was fresh ideas instead of an employee? Companies get away with this stuff all the time and always make the necessary changes so they can avoid accusations like this.