I asked you in post #5 if there were any other symptoms (which related to respiratory diseases) and you stated there were none in post #9.
If your bird had either MG or Coryza, you'd know it. Other birds would be showing symptoms as well.
Here's a link for you to take a look at. Scroll down to Infectious Coryza and then Mycoplasma Gallisepticum (MG) and read the symptoms. Then thoroughly observe for any symptoms your bird might have. Hopefully there arnt any

Let us know what you've come up with.
https://edis.ifas.ufl.edu/ps044