I have no idea who walking man is, and ultimately it doesn't really matter to me; the portraits of him that got inserted repeatedly throughout Google Street View ultimately stand on their own.
But at the very end of his tagalong, there's a shot where he points across the Google Trike's path. He's gesturing, perhaps even to the cyclist/Trike operator himself. Which underscores the possibility that walking man did not just happen across the Google Trike; he may be involved with it somehow, as a tech, or a chaperone, or even the driver's friend.
When I saw artberri's flickr photos [above] of the Google Trike and Buddy circling the plaza at Arata Isozaki's riverfront tower complex in Bilbao, I began wondering if a two-man team might be standard Google Trike operating procedure.
If so, the top of that other guy's head might be a prominent feature when these Street View images come online. We may have a whole series of Trike-based portraits on our hands.