Your first guess was right -- it's the food odour issue. I blanch at the thought of waking up with a bear in my face.

IME, it's hard to clean dishes as thoroughly in the bush as would happen in your dishwasher at home. Plus, many plastics will hold the odour of food/spices even after washing.

In terms of sensitivity to minute smells, think of a bear as a tracking dog. You just can't be too careful.