Very unlikely - unless, separately, you also have a sensitivity to grapes and olives aswell.
Cross-contaminationv is the more likely cause (ie. your olives and grapes have been in contact with a dish / chopping board / knife etc etc that had been in contact with crab)
But then, allergies have such obscure triggers.
My mam also has an allergy to crab, yet lobster (another crustacean) - she is fine with. (Which can make it expensive taking her out to dinner !!) - which is odd since we are an old sea-faring / fishing family !!