I think that is contact and airborne but that type of airborne is from agitation.  I think he would be fine walking by a pile of seeds if he didn't touch them, KWIM?  Could be peanuts, could be the seeds.  Most bird see has peanut cross contamination.

I doubt a doctor could say definitively whether a specific person is contact or airborn sensitive without witnessing it.  There isn't a test, and there isn't a certain level (number) where you cross that line and you are into the contact sensitive area.

That being said......is there sesame seed in bird seed?  I see it is also on your list of allergens.  In Canada the government added sesame to the list of top allergens (must be labelled when added in any amount) not because so many people are allergic to sesame, but because those that are tend to have more serious reactions.  I don't think sunflower is commonly quite as sensitive, but I'm sure it is for some people.

At 2 he probably did either stick his hand in his mouth, or rub his eyes or nose. 

Will you be with him?  I would suggest continuing to limit his exposure as much as possible, and keep an eye for symptoms.  At 8 he is aware of his allergies?  Can he tell you when something starts?  Maybe go through some of that with him, but not specifying it has anything to do with the co-op.  just an in-general reminder about what to do, etc.  (include epi-practice too).

Before our son was officially diagnosed with multiple allergies we were clued-in to the whole allergy thing when he reacted after playing with the bird seed in our basement. He was just two and was loading it into his dump truck and driving it around; something he had done several times before. However he began to sneeze, had hives, red eyes, runny nose and wheezing. Thank goodness my mom was here as she said the little man was really sick and I needed to do something. I think I was just perplexed and didn't have a clue. But after she said that I snapped out of it and gave him some Benadryl, which calmed everything down.

That was years ago now and we are now well educated and vigilant with all of his allergies. He has blood tests every year or two to track levels and skin tests every two or three depending on if we want to introduce a new food, like lobster...yep allergic.

But in retrospect (duh!) just recently, it dawned on me that he could likely have contact and or airborne issues with sunflower seeds. Sure, when he was two he could have put his hands in is mouth and ingested some --highly likely. But how do I know for sure, one way or the other, in a safe way? He just turned 8 today.  Would it be expected that his allergist would have said to avoid contact if that was the case? We do limit is contact anyway, but he is now at risk for exposure while attending our home school co-op. they have asked families to leaves all nuts and sunflower seeds at home. But homeschoolers can be pretty independent minded and not comply or just forget.