I really don't know. Ithink of the possible reasons he could have gotten sick, we can eliminate teflon, avocado, chocolate, a cat/dog, air conditioning, other smoke/fumes. There are preventive measures against these things, or he wasn't exposed to these. If he was, he would have died immediately.
He could have gotten sick from some millet that he ended up throwing up once and after throwing it up he refused to train but the thing that I don't understand is that there was over an entire month between this and him dying.
He was also exposed to other birds where he could have potentially picked up an illness.