OP here.
Thanks to everyone for the support! My son has been taught since we have known about his peanut allergy that her should never eat anything without asking mom or dad (or his teacher) first. I guess we have become complacent since home is peanut free, friends houses are peanut free, school is peanut free and we have had no accidental exposure for 4 years. Anyhow, DS is doing fine. Talked to his GP and allergist. They both confirmed allergy is probably still there and that the reaction was mild because since he was not in contact with peanuts for so long his antibody levels (IgE) to peanuts is probably very low. Now if he was in contact with peanuts again in the near future, it would be a whole different story. So we will be going for a blood test then skin test and if he passes both (IgE very low and non reactive skin test) we will undergo an oral challenge in the hospital. Someone asked why DS has not been tested since he was 18 months. Since peanut allergy is usually lifelong (very few people outgrow it), the only reason to retest is to see if the antibodies are low enough to risk an oral challenge. Our allergy specialist advised us to retest before DS started school this year but I wanted him to get used to school first.
Someone asked about WDW and food allergies. For us it has been wonderful. One of the chef at Chef Mickey even went around the buffet with us to let us know what was safe for our son to eat! Just let them know when you make ADR or when you get to the restaurant.
All allergy testing will have to wait since DS, Grandma and I are leaving for a week at WDW on the weekend!