Pick off play at 1B

[onetime1]

This weekend at the annual Labor Day family reunion picnic the following occurred. My dad is a right handed thrower and on the mound proceeds to give up a beauty bunt single to my little brother who overruns 1B and twists his ankle. My stepmom comes on as the pinch runner and is the tying run with 2 outs in the last inning. The right handed pitcher then comes set with his chest facing 1b and his left foot on the rubber like a left handed pitcher would normally do. He then proceeds to step off with his left foot and does a snap throw to 1B with his inside right hand and picks off my step mom bigger than life. The place erupts and I am not quite sure if we will continue to play baseball at our picnics anymore after that heated argument. Was this a legal pick off play?