Looking for a science fiction novel which starts with an older man on a park bench having a conversation with two or three youths (I think young men, teens). It is a philosophical conversation, mostly about economics and society. The interaction is recorded via a smart device, and uploaded to the worldwide network; it becomes enormously popular, the old man becomes quite wealthy and the teens are viewed as somewhat famous (infamous?) for their part in the conversation as foils, even decades later. This may have been a novella or short story, as well, and may have been by Vernor Vinge or David Brin; it would have come out after 1990 or thereabouts.