funny stories.
you'll laugh, but how I've always remembered that left pedals are reverse thread is that I recall the stuff like your grandmother and how "left " was "wrong", and that's how I remember it's not "normal"
At least we know about it from experience. one of the bicycle shops I worked in was owned by an old machinist and we had crank arm Hela coil kits. The left crank arm was the most common repair. Left hand threads are also common on fittings for gas lines.