That video is legitimate. Watch it. It has to do with keeping the outside foil towards ground or the lowest impedance of the two nodes being coupled. This was fairly standard in the golden tube era. Most of those nasty paper wax capacitors has the outside foil lead identified. With lower impedance solid state circuits it doesn't really matter so new capacitors are often unmarked. But with Mr. Carlsons test jig, you can still determine the outside foil lead. And yes in some circuits it makes absolutely no difference.
Mr Carlsons lab is a good channel. You can learn a lot there.