@Keystone
I remained at the posted coordinates for 15 minutes. Nobody stayed there till the end of event. According to https://www.geocaching.com/play/guidelines#cito there is nothing like the owner must stay there for 1 hour.
I have CITO listing that says what is the route for cleaning, I have map there, I have Waypoint - end point there (in map, in gc.com in waypoints). I did regular announcements that I moved, where I was, etc. The geocacher claims nobody was there.
So OK, no signing to logbook but how can I know somebody was really there? Should I next time write down their nicknames?