Sorry for your loss.
Coryza often causes inflammation of the nasal passages and sinuses usually resulting in lots of discharge coming from the eyes and nares. Face edema is usually seen too. I see you bird looks to be lacking both of those symptoms, so I'd be inclined to think something else. However, I'm not totally ruling that possibility out.
How old are these chickens? Have you added any birds to the flock the past few months? Are their crops empty in the morning? Could you open their mouth, and check for any lesions or plaque deposits? How do their feces look? Have you checked them over for signs of mites/lice? Could you provide us with your general location?
To clarify, the chickens are sneezing, but, not wheezing or producing amounts of discharge? If there are any other symptoms, please let us know.
Do you still happen to have the body of the chicken that passed?