Peanut Allergies

The tragic death of a teenage boy has been reported today. He died after eating a couple of mouthfuls of spare ribs cooked in a peanut sauce. The headline said that he was allergic to nuts. My question of the day is that peanuts are not a true nut, being a member of the legume family along with peas and beans; therefore are people allergic to peanuts also allergic to other legumes? What is it about peanuts that make them so lethal? You never seem to read about people dying after a mouthful of peas.