I think the article is implying that heightened defenses equals heightened false positives. Peanuts would be a false positive to something else that is actually

I think the article is implying that heightened defenses equals heightened false positives. Peanuts would be a false positive to something else that is actually harmful. So if you have an allergy to peanuts it means your body is primed to defend against something in which peanuts are only a side effect. The author implies that if you have allergies, you have better defenses against other things.