This all sounds concerning.
Things that stand out to me are:
Your cashews had a warning on them. Could the cashews, or whatever was the warning, be what caused the reaction?
Was it that you had the equivalent of 1 cashew total? That isn't that much, and it sounds like the level of reaction, if you were having it in any other place outside of the allergists office, many would say an epipen was in order.
I also am not quite sure how you shouldn't be concerned having vomiting, diarrhea and GI pain after eating such a small quantity of a suspected allergen.
Every reaction is different. If it was the cashews, not whatever the warning on the cashews was, I think I would be pretty concerned either way.
What was the warning for on the cashews? Was it for peanut or other tree nuts, or a 'may contains' type thing?