Someone filmed it
Incidentally, a woman in a cab across the street happened to stop at a red light right in front of this exchange of kindness. She noticed the jogger and the homeless man talking and decided to take out her phone and film it.
She didn’t know how this interaction would end, of course. Joe, on his end, noticed the woman recording them and suspected that the whole thing was set up by the jogger, to post the video and earn some fame.