And from the "latency" of the attack ( from time of eating then going shopping etc ) that sounds exactly like the NUT allergen- insidious in that regard.
My child luckily outgrew her peanut/tree nut allergy- Dr. El-Dar drilled into us from day 1 that THE NUT allergic reaction can set in 4-6 HRS AFTER INGESTION ( her Milk allergy will be instantaneous ) Ugh i cant tell you how many times we would eat at kids party or some place new and literally be on edge for 4-6 hrs after.