I would bet, especially if it was Chinese, it was the peanut allergy again.
We have pretty much stopped getting any Chinese, Thai, Indian, etc. from restaurants for takeout. They often use peanut oil or peanuts/other nuts in their cooking. Makes me sad because I love food, but better to give it up than to accidentally cause an anaphylactic reaction.
Noodle & Co. makes all kinds of dishes, and the cross-contamination in their kitchen from the peanut dishes/utensils/counters is probably what caused it. I would say to stay away from that restaurant as well.
However, some people do develop allergies to citrus.
If you do decide to dine out or get take out, call and talk to the chef or restaurant manager first. Explain the issue and ask if they use peanut oil or other nut oil in their cooking or any nuts in their recipes. Peanuts and other nuts are often cross-contaminated, since most nuts are all packaged in the same facilities.
Please talk to your child's pediatrician, and ask for a referral to a pediatric allergist or immunologist. It sounds like your son needs additional allergy testing, and that you need to start carrying an epi-pen for him, until he's old enough to do it himself. Start coaching him now to ask "Do it have nuts in it?" to any food that is offered. If it does, or the person doesn't know, then it's a no-go.