No foul odor usually means it's not coryza. If it hasnt spread to other birds and there isnt other symptoms showing in this bird and other birds; such as head shaking, bubbly eyes, wheezing, sneezing, rales, runny nostrils....and his other eye is NOT swollen and neither eye has bubbles in it...it's not MG. Also if this were a respiratory disease, 2 weeks wouldve been plenty of time for your other birds to get infected and show symptoms.
If it's none of the above what I mentioned, then it could be that he may have got pecked real hard on the lower part of his eye to cause the severe swelling.
If it's none of the above what I mentioned, then it could be that he may have got pecked real hard on the lower part of his eye to cause the severe swelling.