It’s definitely not highly unlikely, at least in my case. My father regularly beat me because I would play a highly aggressive attack strategy and totally ignore what was happening to my king. I’d do something like put my queen on the same diagonal as his king, only to have him take my queen with his knight, simulatenously mating me.
Of course, my father was about 100x the chess player I was. In the commercial, it’s supposed to be funny because the kid is obviously the better player
Actually, in tournament settings, it’s customary to NOT say “check” when the opposing king is in danger. Tournaments are timed affairs and if your opponent doesn’t notice the check, he’ll waste his time thinking of moves that don’t involve removing his king from danger. Of course, when or if he tries to make an illegal move, you then point out the check to him, but by that point the damage has been done.