Probably unrelated but if you have a manual gearbox, with a clutch pedal, when you are about to stop, you disengage the clutch to prevent the engine from stalling.

Clutch pedals are operated with the left foot and meant to be fully depressed. If you are used to drive stick and switch to auto, you may accidentally hit the break hard with your left foot, as if it was the clutch.

So if you see someone breaking hard at the red light for no reason, especially if it is a rental car just out of the airport, it is probably the reason.

I did it, Most of my (European) friends who rented a car in the US did it too.