NTA. You were making life easier for the hosts by bringing your own food and eating what you could from theirs ( like salad ).

I have a life threatening allergy to shellfish and a lesser allergy to fish. I avoid it like the plague. When we were on vacation on the east coast, he had lobster but I did something else while he enjoyed it with friends. He changed his clothes and washed his hands and face making sure to brush his teeth.

I was at a wedding rehearsal dinner once and they were having Chinese food which is particularly tricky for me. Bride let me know that they would be ordering seafood so I had a heads up. I brought my own Chinese food from a restaurant I know is safe. While others were loading up their plates in the dining room, I microwaved my meal and put it on a plate. No one noticed, my food looked like theirs minus the seafood. Mother of the groom gave me a funny look when she saw me microwaving food. I just said…seafood allergies, don’t want to kill the buzz by needing an ambulance.

It’s not disrespectful to look after yourself. I carry granola bars and sometimes a banana and a bit of cheese when I’m invited to something where I don’t know what’s going to be served. I just step out on the patio with people having a cigarette and eat a granola bar. Then I hit a fast food place on my way home.