Those are selected and/or scripted, but are absolutely hilarious and sad at the same time. Jay Leno was doing the same 30 years ago. Candid Camera was all the rage in the 50s.
Victims of the Candid Camera pranks would be told, "smile, you're on Candid Camera." When we were teenagers, we would secretly record conversations on a small reel-to-reel tape recorder and then announce, "laugh! You're on Candid Tape Recorder."