I don’t see how the confusion of brake and throttle could have caused this.
But, in any case I not only have braked with my left foot since 1973, but believe all older people should be taught to to that. Older people, perhaps I should say elderly people do lose the ability to tell where a foot is.
When you brake with the right foot, those feet are moving constantly, and any move could involve that error.
Teach older people to brake with the left foot, and when they get in the car, carefully place each foot where it belongs, and visually verify what you have done.
For those who feel strongly against braking with the left foot, several years ago, we had a cable guy van driver who was taught by a hired consultant to brake with the left foot for all the reasons I do.
One reason not to is if a driver changes from manual to automatic, of course. But, one person once said he does that and has no problem braking with the left foot on the automatic, and with the right foot on the manual. I would not have assumed this.