Oviously, you use same foot for brake and accelator, right foot. The main reason is brake and accelator should not press at same time. The output is zero.It should be press simultanously.

I know someone, who  uses both foot. what i think is those who learned driving from nepal and drove few weeks those poeple use one leg (because of manual shift). And those who learn here generally use both legs for brake and accelator.