At the end of episode 507 "If it bleeds it leads", there is a man who threatens Theresa Lisbon in her office to back off a case. He claims to be from Homeland Security. He then shakes hands with Patrick Jane and says "Hello Jane", and Jane asks "Do I know you?" and he responds "no, but I know you". in the following episode, Lorelei says to Jane "I am surprised that the two of you didn't become friends from the moment that you shook hands." and Patrick takes up this line at the end of the episode saying to Lisbon that the person is someone that he knows.
That person is the random man that walked through at the end of episode 507. They wouldn't put him in there if he wasn't important somehow, other than a treat to Lisbon, that would be trail off plot line.