Our minds like to categorize things, but nature doesn't really give a shit about stuffing things into convenient cubby holes.

Where I am I've never heard of 'nut allergies' including peanuts, but people with allergies to peanuts (and other legumes) specifying peanut allergy.

My wife is allergic to peanuts, lentils, chick peas, etc, but not almonds and the like.

As one commented mentioned these "nut allergies" can be psychosomatic, where the mind is literally triggering the physical reactions based purely on expectation.

On the other hand "nuts" including peanuts are typically processed in the same facilities, so cross-contamination is real too.