My best guess is that as an author, he is thanking his agent - the person who is responsible for finding a publisher to publish the author's work, and negotiating the payment they receive (at least, I assume that is what agents do). So I guess that John Smith is the author's agent, and the use of 'summa cum laude' is a way of saying the agent is superior to all others. I also suspect the author is American, as I believe this title is used in American universities. Someone else might have expressed the same sentiment by saying '..John Smith, agent extraordinaire'.